OP, I mostly agree with what you’re saying about Android. I’ve been a user since 2010, and development of mainline Android stagnated about a decade ago. Google isn’t really trying very hard anymore. I got an iPhone this round as my main device. I still have plenty of other Android devices as well as my last phone (OnePlus 8T) that I will continue to use, but I’m enjoying most of the change in user experience to iOS. It’s smoother and better thought out in most respects.

If your device is really that slow though, are you sure the battery is good? They will definitely slow down when the battery ages to prevent sudden shutdowns if the CPU were to try to use more power than the battery can supply. I think that a bad battery can do the same even if it’s not old.

If not that, how is the custom ROM scene for your phone? That may be a solution if it’s possible. Manufactures like Samsung sometimes go overboard with additions to the OS that just screw things up. Samsung was probably the worst offender in this regard back when the first Galaxy devices launched.