There are two serious limitations to this approach:
1) Tiers only represent the potential for a class, and even then, tier power isn't consistent across all levels. For example: non-casters are actually pretty solid at low levels, and wizards and sorcerers have more serious limitations. A player running a blaster wizard is going to function differently than one who specializes in Conjuration, despite them both having written "wizard" on their character sheet.
2) This in no way takes into account multiclassing. PBs and LAs are taken at character creation; multiclassing happens afterward.