Conjuring up the dead has nothing to do with what I want from a necromancer

Ok, that's wild to me. To me that is, like, the core of the necromancer.

I want a necromancer to be closer to a blue mage than a conjurer

I'm afraid I've never played Magic, nor had any interest in doing so. So I don't really know what the different colours represent.

pulling up a frankenstein of a minion from the component pieces of what they find on their adventure

Oh that's interesting. It sounds to me more like a kind of magi-tech character that might fit something like an artificer. Because it seems like an interesting idea, but it's not the core of a necromancer to me, and even though it does technically involve reanimating the dead, it's an almost mutually-exclusive concept with what I think of as a necromancer.

I find this fascinating overall, because it sounds like there are two entirely distinct concepts of what it means to be a "necromancer".

I kinda hate that the thralls explicitly can never take actions

Yeah ngl I agree with this 100%. Definitely want to be able to use those temporarily-raised undead to actually do things.