Congrats on the very comprehensive guide !
I've played a lot of Insanitary and have tried the summon plan but realised it is a trap. You say it yourself, you have to hire 10+ stones of models you don't want to summon a not so good 7 stones minion per turn with a lot of constraints and a high likelihood of being screwed by the black joker.
On the opposite, focusing on the Appendages upgrades to improve the keyword models has worked a lot better for me.
And for me, the Extra Fat on the Corpse Curator is the one with the highest ceiling. Consider that every time the Corpse Curator moves, it can move a Sludge marker and deal 1 dmg and Poison+2 to all enemies touched by the marker at the starting and ending position of the marker. If this move was caused by Desperate Plot, you get some poison on the Corpse Curator and a built in triggers for more damage and poison on enemy models. And finally, the Corpse Curator can choose to inflict the damage it would suffer from poison to a model in base contact (end of turn or bonus action from Chihuahua). That's a crap ton of unresisted damage.
And that's just one example of what can be done.
Anyway, even though I disagree with your assumption that Insanitary should be played as a summoner. I salute the hard work that was put into building this very comprehensive guide. I just wanted to highlight that there might be different approaches to play Insanitary that maybe could better match the playstyle of some folks reading this.
Thanks again for your work !
Max