Ikari Broly starts to overpower SSG Vegeta. Goku steps in and gets smashed. Until he goes SSJB.

Frieza, the bastard that he is, kills Paragus and triggers Broly’s SSJ transformation.

SSJ Broly then proceeds to outclass SSJB Goku and Vegeta. They escape through Instant Transmission, then Broly proceeds to beat on Final Form Frieza and then Golden Frieza for an hour.

Goku and Vegeta had to do the Fusion Dance. Gogeta went ahead and defeated Broly, but not before using a barrage of his strongest attacks because he’s really that extremely durable.

Goku himself says that Broly was much stronger than him alone so during the movie they had no way but to fuse to defeat him.

Goku, Vegeta and Frieza have theoretically surpassed Broly by a huge margin because of TUI, UE and Black Frieza ever since. To be honest I’m thinking Frieza’s now the current strongest mortal in Universe 7.

To catch up Broly needs to do more than training. He has to first gain access to his forms without going insane. Master them the same way Goku and Gohan mastered Super Saiyan. Train with the Yardrats for Spirit Control. Spar with Jiren so he can learn the Relaxed state of fighting. And then get his potential unlocked.

Finally, though he may not need it, a new form can also be unlocked in the end. This is a fanart of Brohan (Broly + Gohan) but the concept of Full Power Super Saiyan Beast (FPSSB) is just so cool to me.