I have a small pile of Android phones of various ages and price brackets (gotta test stuff, y'know). Throw in heaps of Thinkpads of a certain vintage. IME, it's the age of the software that predicts browser performance much better than hardware. A 6-year old flagship phone that's stuck on Android 8 is a hot mess, while another one of the same age and similar specs on Android 10 runs great. Not sure why, but it's a consistent pattern across all these devices.