In India Or anywhere it's usually mothers have upper hand and they win cases mostly as nothing equates to mother's love not even Father's wealth. Mother's case becomes even more strong when she has life partner to give fatherly love to her son. Again this is ITV, so the only convenient argument was financial status.
I'm feeling more bad for Abhinav here as he lost the family he had earned. He will feel guilty to a great extent just because he isn't rich. But i again don't understand ITV obsession with wealth and richness. I myself belong from humble middle class was still raised with everything my parents could.
If Judge had concerns about education and life of Abhir, I'm sure Abhimanyu could help him with school fees Or college fees too as generally fathers do help in divorces. But snatching a son a life who is so small had heart surgery not to forget and keeping him fir himself is cruel.