I think you not only hit it with Peri being a returning character with SO MUCH to fill in with how he interacts with other returning characters, but Dev overall has a lot of complicated emotions that just never get explored (or is so limited that it's a lil frustrating). like, even his and hazel's friendship gets to sit backseat unless it's a plot relevant ep. Dev and Peri also got shafted infinitely harder so ofc people are gonna write a whole load of 'what-ifs' and their own goofy projection stuff about what wasn't shown.
(and lmao... even when people do create art surrounding hazel, it inevitably comes back around to her focusing on other characters issues... RIP girl was sorta characterised hard like that)
at the end of the day it'll be the usual generalised fandom complaint that there isn't enough 'content', rinse repeat lol... just seems more of an evil constant these days. :'D wish people could just try to make the things they wanna see instead of pointing fingers.