Word of warning, 3d printed cases are a bad idea. The plastics don’t actually absorb the impact like a real case would, and so they break often and don’t actually absorb the impact and protect your phone. Every time I’ve used one I’ve ended up with damage.
Did you use TPU for the prints? If you used PLA, that really was a bad idea. With TPU my drop tests (not on purpose) were successful and the phone without damage everytime (so far)
I get your problem, yes. I also tried printing a bumper for my work phone in PLA a couple times before I was able to print TPU and it always took like 2 weeks until it broke. Those materials don’t like being put under pressure permanently. I didn’t try PETG, could imagine it to be a little better, even though it won’t absorb any impact if dropped.
It depends how thick and soft the tpu is. If you have a thick enough and soft enough case, it will absorb an impact. Just like silicone cases do. And they are also solid.