I think I might argue against Tier 0 existing....
The main distinction I make between Tiers 1 and 0 (or -100 where some of them belong) is use of power and access to capabilities rending one untouchable. Any Wizard 20 can go Pun-pun. Statistical fact. Will he? Only if the party needs a hero, or at least that's how I run it. The Tier 0's have the true capability to become deux ex machina, complete with DvR if they want it, and go Raistlin on the pantheon should they grow tired of divine meddling. And it's not just Wizards/StP's/Psy Arties etc, an Ardent 10 can stalemate Pun-pun and Azriel both, due to infinite actions both forward and backward in time, as a single example. Build the right combo on a Psi-Arty, he can do it too. Same with the right build of Wizard, and even easier as an Erudite (though the SCM can arguably ass pull all of these tricks, thanks to Shadow Miracles being THAT BAD ASS).