I don't think cases should be damaging the phones at all. If that is indeed what happened, then Apple made a mistake with the colored Ti models. All those phones should be replaced or a refund / full store credit given to the buyers. This is what happens when a beancounter like Tim Cook is the CEO.
This is my 14PM that I bought in September 2023, a few days before the launch of the 15PM (deliberately). I went to the Apple Store on the 15PM launch day and I was utterly disappointed with what I saw. Only the Natural Titanium finished looked appealing.
This is what my SB 14PM looks like today. I've used an Otterbox Symmetry case and this is NOT a soft case at all. It is somewhere in between soft and hard but leans to the firmer side. When I first got the case, I was afraid it would damage the phone because it was so strong. But I'm glad to report that my 14PM is still flawless (except for a few scratches in the screen). Note: Any white items you see below is just dust & debris, not marks / scratches.