It is both the story and the actor.
The story is at fault because of the plot. The entire plot is such that Virat is now an irredeemable character.
The actor because of his extreme emotions. It is both the reason why there are people who still ship SaiRat and why there are those who now don't even want to think about them ending together. In my opinion, NB, whose best expressions were the nuanced ones, has indeed lost (or stopped doing?) those nuanced expressions.
When he has to show that he loves Sai, he gives the expression that she is the most cherished person in his life (which is why it is so easy to again start shipping SaiRat just by watching a single scene of them together).
But the issue is, that when he has to show that he cares for Pakhi, he again gives the same expression.
When he has to show that he loathes the person in front, he gives, in my opinion, a pretty decent disgusted face. But when he has to show that he is angry with Sai he again gives the same hatred-filled expression.
Neil doesn't understand how to give intermediate expressions. He himself is unable to show the difference in feeling that his character has towards Pakhi and Sai, so, the audience can't differentiate either.
Acc. to the story, Neil's expressions should be:
for Pakhi (care): Caring but at the same time a little distant and hesitant. The most important expression: pity (NOT love)
for Pakhi (angry): disgust, and loathe. Perhaps even disbelief, and self-disgust.
For Sai (care): Gentle, loving, passionate, and longing expression. Perhaps even pain, for he wishes to touch her, and to be with her, but he can't.
For Sai (angry): Hard expressions, but full of pain and hurt. NOT disgust, or hatred (even if his words say otherwise). The thing is we have control over our words, so we can modify them to make sure the person in front is thoroughly hurt. But we can't control our actual feelings. So, it makes sense if Virat's words are brutal, but his expressions shouldn't be.
But what Neil does:
Pakhi (care): Love
Pakhi (angry): Hate
Sai (care): Love
Sai (angry): Hate
And thus the entire audience goes: 🤓