The fact that his shards are so incredibly difficult to get to 600 keeps him bouncing between SS and A class.

Tiers are based on how effective each unit on max level wtf are you talking about?

if you would keep reading under the tier list, he states that he consideres the shard availabiltiy.

They shouldn't consider it though, that's missleading, main concept is literally rate the character potential

This is actually true, the tier list should be considering how powerful or helpful the unit will be for the player disregarding the shards. they should create a new tier list for characters shards considered if they still want it.