Mono Black can run a minimum of 12 “Destroy Target Land” spells at 3cmc, and has access to Dark Ritual. Sinkhole is super overkill next to that.

You also have to consider that bounce lands are a huge part of Pauper. Decks like UB, RW Monarch, and Tron all stumble easily enough off the current available land destruction.

Sinkhole is absolutely not a good choice to put in Pauper. It’s just too powerful at one less mana. The metagame isn’t healthy with sinkhole just because aggro decks can run off one or two lands. Why would I want to play a Pauper where I play aggro or Delver, or just pray I’m not up against Sinkhole.dec?