A Tier 0 commander is most of the time a partner commander or a 5 colored commander
Now, in fairness, we've recently seen that Pokmon Pocket decks featuring only two Pokmon can be successful, especially now that tools like Rocky Helmet and Giant Cape can make individual Pokmon significantly stronger
Greninjas broader international fanbase could drive a similar trajectory
Blue Otters, Frogs, Birds, and Rats are based in blue mana, and bring with them all manner of spellslinging and flying strategies
lol, almost forgot this is a top 5, ok
Some Modern decks, like Jund and Burn, almost naturally meet this criterion as is, and getting a free 2/1 with First Strike out of the deal is well worth it