I've never used a phone case. I don't understand why they make these things so small and then everyone just slaps on an extra couple mm. What's the point? If we're making them bigger anyway, at least use that space for more battery.
Anyway, the wobble is real, and sucks.
I run caseless too and would be willing to sacrifice a few mm for better durability and no bump. Plastic is fine too. Bring back designs like the iPhone 3GS which were curved to fit your palm and if dropped would just bounce and tank it!
Remember soft touch plastics? Grippy and didn't waste all the space of a case? Then some dingleberry marketer decided slippery metals and glass were "premium" and braindead phone reviewers happily parroted that crap and now everyone buys several mm thick cases made of soft touch plastics to cover up the "premium" materials they bought. Sigh.
I do. My HTC Amaze had nice soft-touch plastic on top of an aluminum back, was slim (for the era) and grippy. Also had a Galaxy Note (forget which one) that had a leathery soft touch back, was very nice. The physical design of phones definitely peaked long ago...
Similar, but I did use a phone case once because it came with the phone and included a pretty big feature. The LG V60 with dual screen case.
It made the phone entirely way too thick. But it was still thinner than the 2 phones I was carrying around previously.