I, too, am a little bit confused by the purpose of this.
I once accidentally the entire dungeon with a lvl10 straight half-orc fighter. I was bored, it was a one-shot, and the DM wasn't much of an optimizer. long story short, spiked chain + PHB and PHBII fighter feats killed it all without a problem. hell, most things didn't even survive my single charge attack, with cleave dealing with the leftovers.
you don't need a class tier system to justify a character in a party. level of optimization is entirely separate from tier, and is what is relevant. I'm sure any min/max regulars could make a tier4 that far outstrips an idiot's tier1 char.