I wonder what metrics provided by fediverse are actually reliable. E.g. views count on PeerTube videos are not, they can be adjusted by instance admin to his liking, lol.

Nothing. All points randomly placed on a 2D plane, then forces are applied to them - all points are trying to move away from each other, but if 2 points are connected with an edge - they are attracted to each other. Check out this interactive demo of force-directed graph

Try image with white legend in bottom left corner.