I used a Lenovo P2 (android 6) for 5 years and I never had any problem so I don't understand why people want the latest updates or they suicide?Is there an updated (2021) list of which phones are easier to root / Unlock the bootloader / flash a ROM? I'd like to buy a phone that'll last me for a few years, I don't like to generate eWaste and any new phone more than suffices for my needs.
Do any of the "alternative" brands like PinePhone provide stable daily drivers?
No phone brand will give you more than 2-3 years updates also 2-3 years later we will see even much more powerful and affordable phones, thanks to China.
I believe in the next 4-5 years you will change phone anyways.