I never had a problem with a “flimsy back cover” or it coming off when I didn’t want it to on any of the phones I had. I’m still using my LG V20 from 2016 and it’s fine. I can get a new battery $20 and do it myself in seconds. A big reason why I haven’t bough a new phone is because I’ve been able to do that and nothing that has come out since then has as many features while getting ever more expensive.