It was still necessary in a sense though. Beating Broly was a scenario similar to beating Cell. You must either overkill him or risk him getting too strong to manage. SSB Gogeta was about to literally evaporate Broly. It's possible no other form could've evaporated him.
If he’s not ascending to another level, which I think we all can agree on that he wasn’t, should give us a ideal of how strong Broly was. A SS Gogeta push broly to his final form, Definitely not unreasonable to think a SS 2 Gogeta couldn’t have finish him... not to mention A SS3 or SSG. There’s more than enough proof to show SSB Gogeta wasn’t needed.
There's no proof that SS3 or SSG could evaporate him. The gaps between these forms are super huge and that's exacerbated by the fact that Gogeta is a fusion. Beerus literally left SS3 Goku dazed with a single flick of his finger, then there's Broly who could tank SSB Gogeta's attacks for days. If the gap between SS3 Goku and SSG Goku were 10,000x, then the gap between SS3 Gogeta and SSG Gogeta would be like 1,000,000x+. Assuming Beerus didn't unleash more of his strength against SSG Goku than he did against SS3 Goku, it's safe to assume Broly is much stronger than SS3 Gogeta.
SSB Gogeta had to resort to Kamehameha. Literally his strongest move. What I mean to say is that SSB Gogeta WOULD have never put Broly down if he had continued with bare-fisted attacks. Broly would've simply continued growing. So I then have to ask myself one question. What's likelier to put someone down, a Kamehameha from SS3 Goku or a 5 minute long beating from the fists of SSB Goku? A: The beating, therefore Broly is stronger than SS3 Gogeta.
I think you are of the misunderstanding that this new Broly isn’t the same Broly of the first three movies. After Broly reach is Final form, he didn’t grow stronger after.. Its pure speculation that you think Broly would grow stronger and beat SSB GOGETA.
