I would argue black decks get a bit more out of the horizon lands than the other colors because almost all of them are looking to hit all their land drops to 4 mana and then not get anymore lands. The other colors either want to get payoff for big mana, or operate efficiently at 3 mana and don't need 4. The horizon lands let players increase their land count to hit their drops each turn and stay on tempo without flooding out later. Blue already combats this with cantrips (lower land count), wastes/tron decks do the same, red gets to either operate on 2-3 lands or play looting, and green gets big mana payoffs and can usually afford to play more spell lands (and already has horizon canopy). Black basically only has collective brutality for dealing with flood, which is a card that is usually weak in multiples and thus doesn't really merit an increase in land count. Black also tends to be color intensive with wanting high%of turn one black mana (most black decks are running 6+iok/thoughtseize) and most black decks want to be able to reliably cast lotv or ltlh on turn 3. This means it's harder to play utility lands to help increase the land count without decreasing the action. Death's Shadow also loves these cards. Sure most mana bases get better with the horizon lands, but I think black gets the most out of it.