Ajay wasn't bad in Himmatwala nor was he was great as such. However, his acting was better than a shitty performance coming from an overrated actor where his fans want to compare him to Khans, Akki, Ajay & Hrithik in the acting department.
Ranbir is B Grade actor who can't pull off a massy film nor can he macho type characters like what Ajay did in Himmatwala. I would even dare to say that Tusshar Kapoor's performance from Shootout a Wadala was better than his performance which released that year.
Even Aftab Shivdasani & Vivek Oberoi are more versatile and can act circles around Ranbir.