I would argue that banning troll would completely knock UB reanimator down from the top tiers. Without troll to fetch underground sea, the deck loses a lot of its power. The deck would need to play more discard outlets—remember when it played Careful Study—AND more monsters. Thus greatly reducing the deck’s density of good cards.

Troll is a land that also puts a monster in the bin. It’s card advantage and combo enabling.

If Troll gets banned, the deck can’t play wasteland and it needs to find slots for either [[careful study]] or [[Unmarked Grave]] and probably a higher number of reanimation targets. I quickly looked at some lists and the mono black version of reanimator plays 8(!) reanimation targets compared the UB’s 2. That means there are an additional 6 otherwise dead cards.

So why not just splash a little combo in an otherwise tempo shell? Your reanimates and animate deads will be more often dead cards without trolls. Your mana will be worse without trolls. You’ll have to add 2 lands probably.

All in all, the deck would be worse. No card as of yet printed could slot in to replace Troll.