Broly kept up with full power Blue Gogeta, even if he lost it wasn't a pure roflstomp, it was kinda like Zamasu vs Vegito (anime). They fought for minutes and Broly was getting stronger.
Meanwhile Jiren got trashed by Goku alone. Goku is just a component of Gogeta, so its less than a half of its power. MUI doesn't matter, remember how Goku at his highest form (SSJ3) couldn't hold a candle to SSJ Vegito back on Z, Fusions are absurdly stronger than their components even at base.
Also Frieza was getting tortured and if you liked the ToP so much you should know he's one fun punching bag. There's also the possibility Frieza got MUCH stronger than Goku & Vegeta, at the very beginning Vegeta is worried due to that possibility.