On the first point about the yellowing I know what you mean. Be advised that you'll get that same effect by drying them in a gas (rather than electric) clothes dryer.
While I agree with most of the rest of your post, the second point is completely in error. I too have travelled in the Middle East (nearly a year in Saudi) and wore heavy denim jeans whenever I wasn't in uniform. They performed great. On a more tropical experience, I wore them EVERYWHERE in Panama (TBH it didn't really get any hotter or more humid there than Summers here; it just stayed that way year round there) Again, they performed just fine. However, thin anything will simplt not provide any protection from briers, rocks, scrapes, or bugs. There is nothing better than jeans. Nothing.
I also wore a poly/cotton blend shirt in both cases (60% cotton to 40 percent poly for durability and wrinkle resistance) and in both cases the shirts worked fine.
Not completely in error, it's an opinion so I can't be wrong I also wear jeans all of the time for casual ie indoors and at the mall or pub,I am currently in Kuwait (no pubs here) my weather station says max temp since I plugged it in around Feb was 47DegC, last week it was 89% humidity, the tropics are generally high humidity, in my opinion Jeans are rather sweaty in this heat, my cargo pants are not, my shorts are better but I wouldn't wear them all day on a boat or tropical island for fear of getting burnt, i wouldn't wear them in a jungle, seeing as this is a bushcraft forum I assumed the original question would have been around outdoor activities not sitting in a coffee shop in a Riyadh mall or air conditioned SUV or Grand Indonesia Mall Jakarta,
I have been bitten by mozzies through my Levi's but never through my cargos which are treated, don't see many mozzies in Kuwait, Saudi, Qatar, Dubai anyway
My yellowing comes mostly from a trip to Petra and constant cleaning in Kuwaits water even after filtration, it's permanent, won't shift, maybe I will try to get them dry cleaned anyway I would advise against white 5.11 shirts for outdoor use unless you want to stay cooler in the desert and don't mind the stains
One other thing I would say is you can buy Tshirts for next to nothing in SE Asia, India etc, you can almost wear once and recycle, save on luggage space, carry on and avoid breakages
Big name brands have big name prices, damage is expensive, just make sure you have loose fit and plenty of ventilation
Dano