Oh! Haha ^^;; well while ıts mix of my opinion along with story..
spoilers !
Well Simon is type of a guy who looks like has strong logic but beneath that look he has rather very strong emotions he keeps hidden (or at least he tries to while failing time to time) so when he sets his mind to believe he can finally save the humanity thorough searching main character's unique powers and try to create medicine for everyone.. thats exactly why he acts super stubborn towards any type of convincing's because he was on that table many times too in hopes of finding cure (well maybe not literally on the table? but he does sacrifice and donate his body for researches and this is why he has so much separate body parts barely being attached to together by stitch.)
But ı get what you mean with Isaac ^^ I guess once you pass his delulu dinner event he rather softens quickly towards you! well good news is he would be very happy to hear these from you either. I wish you a good time with him in next chapters :)
edit: oh well- anthony can be kind of scary (and sneaky) in other's routes so you need to be careful about him ^^;;
I haven’t tried Anthony’s route yet but I’m pretty sure Issac beats them all out no completion
Maybe Anthony will win me over but that means he has to be nicer to me than Issac which will prove a bit challenging. I’m interested to learn more about all three of these messed up characters because even if Issac is my favorite, he far from an Angel (Dw Issac you’re still an Angel in my eyes💕)