Can't comment on the available compounds either as I don't know. And we've got cars from 3 different sources/creators in use here. So that alone makes some differences. But having less compounds makes it less work to balance things out as already mentioned.
As for making tyres last they the key is thermal degradation; the hotter you run the tyres the more they will wear down. Thermal degradation kicks in before the optimal tyre temp for grip but obviously you want to keep the tyre temp at a point that offers most grip. But when you get over that temp you lose grip and the tyre wears down faster. And as the tyre wears down it'll have less grip and it's easier to slide it and that also makes it easier to overheat it.
You were overheating the left front tyre and that lead to excessive wear rate. You need to be especially careful the longer a corner is. At Road America the main "problem corner" is the Carousel. Left front temp can easily sky rocket there if you push hard all the way around it. And then it can't cool down much before the kink that is also pretty hard on the left front.
My Motec data from the race is actually pretty useful in showing and explaining this a bit. At the end of the race I wanted to see if I can push and get the fastest lap from
@Mark Breslin Most of my laptimes were in the mid 04s throughout the race. But when I pushed on the last 3 laps I did a 03.9 and a 03.3 but then the last lap was a 04 again as the left front especially was too hot and it just didn't have enough grip.
Mark already wrote some tips on how to drive the car differently to not load the outside front too much. Of course balanced setup is also important but the outside front tyre is still the one taking most of the abuse.
Hope this helps
Edit: Forgot to go through the Motec data pic
As you see I somehow managed take a ton of wear out of the left front on the outlap! But it must've happened when coming to the grid as I drove smoothly all the way around until then. I got a bit of a flatspot too which wasn't nice to have right from the start!
The left front is wearing out fastest every lap but on the final laps it's increased and you can also see the temp curves go up for the last 3 laps.