I have the Caudabe Sheath on my 13 Pro. I just tried setting the phone on my desk and using it, went through several different apps. It will wobble if you deliberately push firmly on the upper left hand corner of the phone, but while using it normally it never felt wobbly or unstable. The light touch/taps needed in normal usage of the phone don't affect it in the least.
Sure, if I'm going to sit here and purposely and repeatedly push on that upper left hand corner I can make it wobble - but I'm not that OCD about things. It's plenty stable in actual practical use, unless you're using an app that makes you forcefully push down on the top left of your phone over and over.