[Reelin]

Unfortunately it's complicated. There are many OEMs, and each configures things to their liking. Then there are carrier branding deals which (often) result in per-carrier customizations on top of that.

Typically, "uninstallable" apps can be disabled via adb commands if you don't want to (or can't) flash a custom ROM. Sometimes they can't however - for example, Amazon sells subsidized phones that display advertisements on the lock screen.