The irony is that early Android phones were built to last, but quickly got obsoleted by more recent models. Now, progress is much slower, but the thing that kept devices alive (removable batteries and community ROMs) are dying. Real obsolescence is replaced by planned obsolescence.
how long is "way beyond OEM updates"? one year? two years? three years? five years? The main problem is that third party roms can only update so much. Without OEM support, you're not going to be getting updates for the proprietary bits of your phone. This includes blobs, baseband, and even the kernel (technically it's open source, but all android phones run off a customized kernel that's specific to that SoC. When that SOC gets EOLed, the updates stop coming).
I have far less trust in a random community. Plus, their EOL could be completely unexpected.
I do not want my phone to be reliant on community updates, personally.