I don't think the issue was that specific unit. Only 1 AC for a unit that size is pushing it, but typical.
If it was 95 degrees outside and my Heartland TT was sitting in the direct sun I'd expect it to take 1-2 hours to get truly comfortable inside. But once it is comfortable, the system can keep up. We spent several days in Tuscon last year without shade and the A/C was on the whole time, it cycled appropriately and worked just fine.
As others have said, you have to plan ahead and manage any RV for very hot weather.
I have my TT pretty well buttoned up right now. Blinds are drawn, insulators in the 2 vents, and a foil barrier for the door window. It hit 104 here yesterday, but this morning it was only 77 inside the TT when I went in to put some gear away.
For the rest of the summer we'll probably be around 100 degrees when leaving home and heading to cooler spots to camp. When we get there we'll open the door and windows, then fire up the Fantastic Fan to pull as much hot air out of the unit as possible. And only if that is not enough to cool the unit will we fire up the AC.
