Hahaha, I like the name :P

Outside of "Pulse of the XXX" cycle from Darksteel, "if opponent controls more blaa than you" has always been : Gift of Estates, Knight of the White Orchid, Linvala, the Preserver, Land Tax, Tithe, Weathered Wayfarer, and Timely Reinforcements. Considering how few truly unique "things" has in its toolbox compared to other colors, it should remain that way IMO. It's part of "equality" theme.

Maybe "When ~ enters the battlefield, if an opponent controls less lands than you, do X"

Fits black selfish theme.

That does sound but it presents couple of new problems.

Smaller one is that it falls into that "win more" camp.

The primary problem is that now it's pretty much just straight up ramp which is not supposed to do. With the "you have less" restriction you can kinda justify it since you're just playing "catch up" and not ramping more than your opponent.

Yep, you're right. I'm not a fan of this idea either but OP is clearly trying to make a mirror Knight of the White Orchid.

And the problem with making a black Orchid Knight is that any additional costs reduce the flavour. Like if you had to sac a creature or pay life or anything else black

I don't know if this is a good idea, but I really love the mirror name :)

Maybe "if an opponent controls more lands than you, they sacrifice a land"? That might be too awful, but seems like a black version of KOTWO.