I was the one who originally made the statement, and that wasn't my point. :D
I meant, there's like 650 Pokemon. If we had small tiers, say about 10 in each usage tier, then by the time we get to NU, yes, of course you can use every Pokemon, but there might only be, say, 70 competitively viable Pokemon in NU, plus the 10 in UU and the 10 in OU, which gives you like 550 Pokemon which aren't viable in any of the main metagames, and about 50 which are viable in all 3.
If you make the tiers larger, you could at least push that number down to 450. Plus, we might have an extra usage tier or two aswell, if there's enough demand for it.
You seriously don't think the likes of Vileplume, Dragonair, Pidgeot, Stantler, etc. are viable in OU, do you!?!