I got this question in at the tail end of the last thread, so I'll repost.
It looks like the Gravity Drill AI is seeding 25-37% of its planets with Gravity Drills. In a small sample, roughly 10-15 planets with one Grav Driller AI. Is that intended? I seem to remember more of them. I just spawned a map with two grav drill AIs and ... I think... 26 Grav drills, and the one after that, 29. This seems a little low for 80 stars and both AIs, especially since they have been nerfed to 32 speed limit. I had a cluster-map where I even thought I had no gravity drills until turning on a game with full visibility. There were about ten.
I don't know whether to update the AI text description, consider this a bug, or request it seeds on more planets, but I'll happily update a mistaken ticket I created to actually be relevant.
Sorry, I meant to reply to this but got kinda distracted.
Anyway, 1 out of 4 with grav drills is quite a lot, though I agree it's not as excruciating as before the gravity nerf.
The actual math is to pick 50%*(diff/10) planets of that player for drills. So 35% for a diff 7 AI. Or between 27 and 28 stations out of 80. There's some rounding and it depends on the precise split between the AIs, etc. But it sounds like the math is working.
I've amended the tooltip to "Aggressive AI with a gravity drill station on many of its planets." which is a little clearer that it's on many, but not necessarily most.