The gun in question is an element Gun, so there’s a lot they could do with that. His element gun is capable of projecting any element he wants. Be it fire, water, earth, wind or lightning.
Of course in the films he just uses regular blasters, which is a shame.
That all being said, Rocket and Groot are the two most popular members of the team, i wouldn’t be surprised if they went with Groot if they wanted a second Guardian rep.
Star Lord stopped using his element guns long ago, they were one of the things that were dropped when Dan Abnett and Andy Lanning brought him back and eventually formed the 616 Guardians (which is still the team’s most iconic run).
I think he used them in the crappy Bendis run, not sure if they were as powerful as retro Star-Lord though.
I think you can do a decent amount to differentiate Star-Lord from Chris & Hawkeye. He could be more “slippery” than those two, being able to get out of tricky situations quickly & I feel his sci-fi gadgets could lead to some interesting stuff. I also he’d be a mix between brawler & zoner.
For starters, Starlord can fly with his boots/gear so he has flight mode by default. Other than that, he’s a gunslinger mostly but has great stamina as shown recently in his ongoing and older comics and he could be even more than Captain Cold with his guns. He can use the normal blasters and the elementals, giving him lots of versatility for a gunslinger.
Problem with Starlord is that if he makes it in, Punisher won’t make it and since Chris is in and Leon probably will be too, along with Dante, Rocket Raccoon and Deadpool, I think is too many.
For Guardians, RR and Gamora will do great with Starlord for DLC as the third option.
Has Capcom confirmed that Rocket is playable? As far as I know they have not. If you omit Rocket you get an even number of six characters per side confirmed to be playable so it makes more sense if Rocket was just meant as a cameo in the trailer.