I agree! Shounen MCs before were full of emotion (naruto, luffy, natsu)
Now being cold and emo is how MCs are
BUT i am guilty of liking characters who are cold (sasuke, zoro, gray, )
Ichigo and Gon are an exception though.
I dont hate the MC personality change, it has become more popular to be nonchalant
cause they aspire to be the dude that can kill all their foes in 3secs flat. the character being flat dont matter to them if mc making flashy moves and got fire fight scenes then they all set.
i suppose its easier to project on a blank slate? but hey what do i know i prefer complex characters and have more than one braincell so i probably wont get it
man idk about the comparision cale here SL mc literally died as a sacrifice got a rlly fucked up life let him heal till he finds joy, MHA the anime and fandom centered around literal teenagers and underlying msg of youth as team? Tanjiro also had a shit life but bruv gotta stay positive so he dun gotta fall apart fan bases dont matter but for real though
i think main trope is the harem kind over killing mcs persona, or the dungeon style where over time they trade emotion, and innocence for power to protect themselves and others

Genuinely curious
Why does shounen fans like their MCs to be edgy and emotionless these days? Like Solo Levelling has a bland MC af with personality of a cardboard. Some of the fans also hated when the MC cried for his mother (that's one of the very few times when he showed emotions by the way) They trash on Deku and Tanjiro, not that he's a masterpiece but why crying is seen as weakness?
Personality is a seasoning to a character. Even worse, when the side characters are just there for the MC. They don't have distinct characeristics so the whole dish tastes bad on my mouth.