That is another really fucking dumb design decision: having high summoning skills affects the stats of summons which are not part of the summon "tree", meaning that someone with high necromancer skill will have a really shitty bone widow with roughly 1.4k HP, while someone with high summon skill will have a 3k HP tank.
The whole game is so great, but it's dragged down by a buggy release and some really dumb design decisions, so easy to abuse character respec, complete lack of balance, what were they thinking?