I never really considered the wheel size as a factor in tire (okay, "tyre"... :) ) wear rate but your hypothesis makes some sense at least intuitively.  But there are so many other factors at work it's hard to draw a clear conclusion.

Road surface: smooth asphalt or English flint?  We did a tandem tour in south central England 20 years ago and between the damp weather and the English flint in the road surfaces ground our tires and rims and brake blocks to mush, much more rapidly than when we have ridden elsewhere.  On that particular trip our bike had one of each: 20" front, 26" rear.  I know the front was pretty much shot by the end but don't know that it was due to the size of the wheel, nor do I recall what was the condition of the rear.

Inflation: are you absolutely rigorously and fastidiously diligent about maintaining proper tire pressure at all times?

Loading: if you use a small-wheeled bike for loaded touring and a bike with larger wheels for unloaded riding, it seems like the smaller tires would wear faster for that reason.  Switch those around and what happens?  I dunno.

Tire compound, and initial tread thickness: In the world of automotive tires at least, different brands and models of tire use different rubber compounds to promote different characteristics: handling, grip, durability... I don't know whether the same is true of bike tires but it's hard to make a direct apples-to-apples comparison because very few manufacturers offer the exact same model across a wide range of sizes.  Even if they did, I've not done the experiment because, for example, I want touring tires on my Bike Friday but I want light weight high-performance sport tires on my Madone road bike.  Horses for courses, and all that...

Over the years I've grown to hate flatting, so I don't push the wear on my tires anymore. I check my tires for slivers, gouges etc after every ride. Those two things are really cut down my flats/mile.

Like Mike Ayling, after the second or third puncture (depending on the mileage on the tire) I just replace the tire.

I've never really seen the benefit of rotating the tires, I just replace the rears faster than the fronts.

All that said, I seem to average 3,500 - 4000 mile on a rear tire on my road bike, probably 4-5'000 on the touring bike with heavier treaded tires compared to the road bike. I've tried various tires over the years, currently favoring Schwalbe Marathon Plus for the touring bike.

George my most recent fully loaded tour was 3820 km across Australia on sealed roads on 26x1.6” Marathon Supremes. As always, they were excellent. 

They could probably have done another 1000-2000 km especially if I had swapped front to back. But I have replaced them in prep for another longish ride. 

One of my co-riders, turned around (at tour end) and rode home, (I flew)  so he did about 8000km on his tyres with a much heavier load than me. Also on a 26” wheeled bike. His tyres were heavier duty Schwalbes. than mine M+ I think but I’d need to check.

On tour I'm on vacation and as long as my tires last the duration I'm happy. What I want/need at my age is safety, efficiency, comfort and as much as possible few or no flats. Most of the time in that order, - unless I just had a flat. 

Continental 4-Seasons are my all purpose road tires now, both for touring and around town. On my old bike I had 28mm front and 32 rear but on my new bike with its much wider rims it will be 32s both ends. So a bit more comfort and not much more weight. No they are not bulletproof but in 6+ plus years I’ve been riding on them, one flat. 

But then I also carrying a second set of tires in my panniers. They’ve been 40mm dirt tires and with the new gravel bike I should be able to fit 45mms. I haven’t pulled the trigger yet but I’m drifting towards the Pirelli Cinturato Ms. When the pavement ends or an interesting trail presents itself I want to be able to swap tires easily and venture on. Needless to say I won’t be going tubeless anytime soon.

https://velo.pirelli.com/en/uk/product/cinturato-gravel-mixed-terrain/700x45c/classic

https://www.continental-tires.com/bicycle/tires/race-tires/grand-prix-4-season

Like others, I don't track mileage (although I suppose I could since I have several bike profiles on my Garmin--but I don't always record my rides).

A tour, for me, almost always starts with a flight.  Then, if I'm going to the expense of flying somewhere, and since if I'm flying somewhere, I'm going to spend some time, I also start with new tires.  Then those tires get ridden on around home until the next tour.

I never ride my tires until the tread is gone.  I want the best grip, be that on gravel, rough roads, or wet asphalt.  Similarly, I don't rotate my tires.  The rear wears, but the front provides control.  When I get new tires, I save any that are in good shape, usually the front, for a spare.  If I should have a major issue and need to replace a tire, it's nice to have one handy in the workshop.  Should my spares get to be too numerous, I donate them.

I've just had my first flat (rear) here in Tucson since replacing the rear Marathon Racer tire. ~2,000 miles. I was surprised at the amount of wear on the tire, although I can see tread all the way across. Rear tire wear is definitely a bigger issue on a recumbent, compared to the front. My front tire looks about the same and it was not new in Tucson.

Ironically, I know exactly what gave me a flat. A broken bottle. I could hear a little tick, tick after I went close to the bottle. I should have stopped instantly. Because I run fenders, it's impossible to see the rear tire without removing the wheel. I didn't. 

I also have to somewhat bashfully admit that I thought there was absolutely no way I could get a flat tire, because only five minutes previously I had given away both of my spare tubes to a homeless man. I thought my karma would be  paid up for my good deed. What is the universe trying to tell me?

The good part is that I did make it the 20 miles back to my lodging and the tire went flat after arriving . . . 

Changing tires on my Bike Friday is a beast. (Schwalbe Marathons but also the stock Kenda Quest tires it came with.) There's a trick to it unless you want to lose all the skin on your thumbs (been there). There are Youtube videos to show you how. It involves pinching the tire sides into the well of the rim.

Do not use tire levers to mount the tires. 

Good idea to replace your tires before your tour. I'm doing the same. 

I've had decent luck with Marathons. They should last the length of your tour.

The cotton ball idea is genius.

My patch kits all have $1 bills in them. When I get a flat, I fold up the bill and cover the hole as I am filling the tube with some air. This keeps the hole from opening and closing, biting the tube and causing secondary flats. When you finally remove the tire you get a little gift when the bill falls out. 

I love the feel of Panaracer Pasellas with Tourguard. The sidewalls are rather weak, however. I had a sidewall blowout on my Tour Easy one night coming home from work. So check your sidewalls for fraying. 

For tours, I only use Schwalbe Marathon Plus tires on my Specialized Sequoia touring bike. They last forever. It's truly uncanny. I put new ones on the Sequoia before every tour just to be safe. As a result,  I have several old ones in my basement with over 5,000 miles on them. They have plenty of tread life left. I use them on my around town bikes. 

Using Pluses I haven't had a flat on a tour. Knock wood. I went DC to Key West (2,000 miles), DC to Portland OR (4,300), and Indiana to San Francisco (3,000) without a flat using Pluses. That's just amazing.

I have managed to get a few flats locally but they were from hitting metal things, like a nasty, sharp screw. Nothing will stop that. 

One downside is they are heavy. Well, so am I. 

Another downside is they are very hard to mount. 

I just ordered new Plus Tours (lower priced Pluses are out of stock) for this summer's tour. 

John,

Years ago I had a flat that wasn't repairable. The only thing I had to use for a boot was my lunch money, a $20. bill. What to do? I went without lunch . . .  the boot worked so well, I left it installed. When I finally had another flat and removed the wheel, my $20. bill was shredded to an alarming degree. I was slightly concerned when I took it to the bank to trade it in. Happily, they accepted it. 

Jacinto says to tell you to go right ahead and tour on those Marathon Plus' in your basement - he has left on tour with them so worn down that a blue stripe shows all the way around! He pointed out (correctly) that even worn down that far, that the tread on his tires is thicker than on my brand new Marathon Racers!