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

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.