The Atari 5200.
It was the successor to the massively popular Atari 2600. It wasn't backwards compatible, it had atrocious build quality (its controllers commonly broke within a week or two) and weak software lineup. It's a big part of the reason why the American video game market crashed. It buried Atari with it. It was so bad that the history of console generations got revised to omit the generation of the Atari 5200 altogether and merely make it a footnote of generation 2, therefore moving the NES from generation 4 to generation 3 and everything else accordingly with it.
I didn't read your OP's reasons because whatever you said, it can't touch the Atari 5200.