All of this happened with BM having zero nerfs. No excuses. Haki on display, devil fruits in full effect. Jinbe is much weaker than Vista, and Luffy at that time was probably about equal or a little weaker.
As a side-note, here's a reminder of how Jinbe fared against Akainu.
Back to Luffy, who also had no qualms about going straight after BM and suffered nothing for it.
Against Bege, it's clearly stated she regained her wits.
At this point, she's not just back in her right mind, she's enraged.
Bege is barely low veteran level, and Vista is nearly 2 tiers above him. Of course he wouldn't have lasted very long, but if he could go that far, Vista could go much farther.