The difference between tier 2 and 3 is huge though, because tier 2 can still be game-breaking and world-ending (just in less ways compared to tier 1).

You can optimize and be an extremely effective and terrifying tier 3 character as a melee-type (especially if you go ToB), but how the heck are you going to rival Timestop or Dominate Monster or Etherealness or Solid Fog or Greater Dispel Magic or...you get the idea. I mean yes there are items, but...

And heck, all the spells I listed are from another Tier 3 class (Beguiler). I haven't gotten to the really broken crap like Genesis and setting your own time trait.