YIMBYism is about telling people who are mad about some structure being built near where they live, and who are engaging in poltical activism to try to stop that construction, that their anger about the structure shouldn't let them stop it from existing.

In this respect there is very little difference between a NIMBY getting mad about a data center and getting mad about a new housing development that will make the area more crowded and use more water.

The only difference is that you yourself are mad about data centers. If you are a YIMBY generally-speaking try to see how the anger you feel about data centers is like the anger your opponents have about new housing, and let that empathy make you a more effective YIMBY.

Honestly, it sounds kind of incoherent to me. How do you imagine YIMBY relaxing zoning and allowing things at lower cost and not simultaneously allowing people with money to push through what they want?

It sounds more like you are saying YIMBY but imagining MIMBY (maybe in my ...) where you've just replaced those other guys making the decisions with your own cabal?