Even if Wizard has 1 hp, he is still Tier 1, because Tiers are not power. Tiers are potential.
You also need a player who understands casters. Otherwise you'll get Wizard who'll be preparing maximized Fireballs instead of Anticipate Teleportation, Greater.
Wrong. You can "contribute" even as a level 1 Commoner.
"People above" are also wrong, since they think only that balance is all-encompassing quality that is applicable in all games under all circumstances. However, their "balance/disbalance" exists only within the specific paradigm. Without understanding this any discussion will be nothing but an endlessly repeating circle of "but I had fun in disbalanced party/but I didn't have fun in disbalanced party".