I got my Model 3 LR RWD in May of 2018 - before the Overheat Protection feature existed. I went through the first summer here in Phoenix just like a legacy ICE car, with the interior roasting in the sunshine. No issues at all - other than the normal "ouch, ouch, ouch" when putting hands on the steering wheel.
Putting Overheat protection on "No AC" will drastically reduce your daily phantom drain, but still keep the interior a lot cooler than without it.
These days, I'm not putting many miles on my Model 3, so I leave "Overheat Protection" on A/C just for the comfort factor of getting in the car (and if I'm really a wimp, I'll set the climate control to stay on when I get out of the car). 16 miles of range equates to about 4 kwh which is about $0.25 at the off-peak rate I charge at.
I'm not concerned about the interior temperature of the car (I've measured air temps of 165F inside the car during the summer, and interior surfaces exposed to the sun at 190F). Tesla is using the same materials and electronics as other car makers, and they've all learned to deal with those kinds of temperatures. The only thing that concerns me is the display - units that size are fairly new in the auto world (other than the Model S, and that one had a few issues...), and I'm slightly concerned about it's lifetime in full heat. On the other hand, I haven't read about significant failures of Model 3 displays, so my concern is probably unnecessary.