That's funny. Saajan gave them equal screen time. Saajan introduces both Sanjay & Salman characters together. It is a proper triangle love story till the end. The screenplay speaks otherwise to your claims. But yes, Sanjay was the bigger star there.
Sunny in Jeet is pretty much accurate. But Salman's role is not an ordinary one. It's his fight, Sunny's characters support in the second half. Not just Karishma's character that acts as a catalyst, it was Salman's which has a strong purpose & ergo gives Sunny a purpose even though the film tried to be the 90s Muqaddar Ka Sikandar.
Hum Saath Saath Hain will always be a Salman Khan film. Like you said, he was the only superstar in the film. And despite all other actors, it was him being part of the film which mattered the most. Do you call Akshay Kumar a supporting actor in Ek Rishtaa?
HDDCS is something you just want to say to provoke Salman fans. He was not the lead. Not a supporting actor for sure. Much of the first half belongs to him & not just Ash.
Lastly, Biwi No.1.... I don't think Ramesh Aravind & Kamal Haasan were in supporting characters. Bollywood obviously didn't have the courage to make a loyal remake instead they added enough stuff to cater to Salman's stardom. It wasn't Karishma but Anil Kapoor who impressed but again it was evident his market was declining & only Salman's name pushed the film initially. Karishma has never pulled a film all by herself (box office wise).