Glover actually set up his TD's against OSP because he could. Cummins didn't have the striking to set his TD's up, really, and OSP would just explode back to his feet when he was taken down by Cummins. He did the same against Glover, but eventually it didn't work as well because that takes a lot of energy.
Having the striking to set up your TD's is a huge factor in a fight. Cummins is a better wrestler than Glover, but he didn't have the striking to do what Glover did. Glover can set his TD's up better because of that, he can make his opponents respect his hands and get TD's on them.
Also, the fact Cummins only has wrestling makes OSP more effective because it's the only thing he had to worry about. OSP had to worry about literally everything against Glover because Glover can do it all.
I wouldn't say OSP wasn't as good a fighter in the Glover fight, it's just that Glover is a far more difficult match-up than Cummins. OSP had more to worry about with Glover than he did with Cummins. Glover is on a whole different level than Cummins is. Cummins may be a great wrestler, but IMO, Glover is the more dangerous grappler because of his GnP and his submissions. He's far more dangerous on top than Cummins is, in my opinion.