Even I can see the logic behind his change. He has a different attitude and a different way of presenting himself. He won't take any crap from anyone anymore. Not that he was necessarily doing that before. (Especially from his Dad). He was always blunt and cryptic with Tej. But with other people he was very laid back. But since his Mother's attempted suicide and all the fall out with Svetlana, he has become more cold and withdrawn. That "fun" side of Omkara is not seen as much.
Considering the situation he is trapped in, I don't see how he can be the same way he was before. That would make little to no sense. But I feel in "essentials" he is still very much the same. That is why despite hating Gauri thinking of her as a home wrecker, he helped her in that crucial moment. Even now, because ChulBul so called "saved" his Mom, he is trying to be extra nice to him. His weakness right now is his Mother, and Svetlana is making full use of that.
As long as they "retain" the old Om somewhere in there and show him to us once in away, we can be convinced he is still very much present. This new phase will continue for sometime, and I hope he strikes a happy medium between Omakara and OSO.