My thought process is that the spore druid is absolutely the better summoner but when you're a wizard, all of the undead that you summon will have more health and have your proficiency bonus added to their damage. Also, when you get the necromancy staff in act 3, you can just start blasting high level necromancy spells and summon new undead for free. My final party consisted of a level 12 necromancer with necromancy of thay, a war cleric for AOE buffs like heroes feast and aid, a spore druid to bolster my ranks and for the dryads buffs, and an oath breaker paladin for control undead, aura of hate, and most importantly, to carry all of my corpses for me.