I don't have any problems with anyone I've played using gunner, the most I get are tent-pitching jokes and a few "Wow, gunner can really do that" responses and maybe a "gunner is annoying". Imo, if your character can frustrate someone, you're doing something right. So what they said gunner is "cancer" or to stop "spamming projectiles", gunner is not even close to being "cancer" and projectiles are a decent part of gunner's moveset and gameplan (but you don't want to be overly reliant on them).
No lie, I absolutely get salted over luma whenever I fight rosalina and have been in that "OMG screw Rosalina" mindset, but it's up to me to make sure I know what Rosa is capable of against gunner and make necessary adjustments to combat her, since I sure as hell know people aren't going to drop her because I complained about her.
Tl;dr - Don't give up on the character because some people are giving you a hard time over it.