As a gunner main who literally ONLY plays Gunner both in base PSO2 and in NGS, Gunner is piss weak at the start, and it takes a lot of money to get the gear and augments rolling too, but once you get to that point Gunner is a monster with optimal use of PAs during Chain Finish. Unlike PSO2, NGS's Gunner leans way more into the ramp-up trait since Chain Trigger is automatically baked into the play style rather than something you pop to put out insane DPS on a single enemy.
But whether or not that ramp-up is worth it is up to you. I wouldn't be playing PSO at all if not for Gunner existing, so even though it absolutely sucked until around level 18, I stuck with it. Then I started seeing some pretty significant gains. Also, as tempting as it might be, don't go for the Crisp bonus if you're PSE Burst farming. Light or Rich are better since you're gonna be spamming Aimless Rain a lot.