Honestly i think you are rigth about it but not because of necromancy. I never played spore but I just found out that he can regenerate the temporary hp. Effective he became for me a troll whit out any downside. This class is insane. I think effectively around the end game its possible to gain like 20+ temporary hp / turn w/o dooing anything. Multiclassing can have even more brutal impact on this class.
Spore druid is hella fun, once you can raise 'spore servants' you get to throw them at the enemy as fodder. Halo of spores (hitting harder the more temporary hp you've got is a chefs kiss).
The best way to play is early is with 1 lvl of fighter (for proficiencies - heavy armor, more weapons, con saves - con saves are amazing cause you can pretty much ensure you never break concentration on your spells) and 11 lvls of druid to get access to the juicy lvl 6 spells (heroes feast is love) and cause symbiotic entity gives you bonus hp based on your druid lvls.
And then in act 3 you get the special sporekeeper light armor that allows you to spread haste spores... now that shit is broken and I am abusing it on my current run with Jaheira (she's basically specced to never break concentration on any of her spells).
And if you are curious how it functions I did post some of the fights on my youtube:
Also, in the Ansur battle I made several mistakes and yet it was still easy.
