Fungal infestation is what needs work. It's the ability that, thematically suggests all sorts of creative play, but totally kills it through an overly narrow and mechanically rigid implementation, that just makes it into a mildly interesting combat tactic of limited use.
When I saw that there was a fungal necromancy druid, I was envisioning swinging through the jungle treetops on the back of a fungus powered giant gorilla corpse, my loyal undead pet ferret Lazarus ever by my side. Spore themed buffs are cool and all, but it's not what makes the subclass thematically interesting to me.
To me what would make this subclass awesome is if I could use the power of fungus to both A) have one semi-permanent undead pet and B) also temporarily reanimate beasts (including larger beasts) and make some limited use of their unique natures. I don't really care if these critters are useful in combat, druids can always summon creatures to help them in combat. I'm more interested in being able to make general utility use out of corpses of exploration and roleplay.
5e Necromancy in general would benefit from having a simple template to create the undead version of a creature, and the idea that zombified beasts come back using standard humanoid zombie stats is where the lack of such a thing really gets felt.