I don't think his acting is OTT at all, he's a phenomenal actor. He's seen his mother get physically abused, and he feels betrayed by Aaliya, one would be extremely angry, and that's how Harshad is meant to portray his character, I think he's doing very well :)
I don't agree with you or anyone else who thinks that Zain aka Harshad is OTT his flawless and anyone in Zain's feet would react like he hid n as for Harshad his acting is phenomenal which keeps improving day by day .