Shooters, as a class, are mostly fine the way they are right now. Not perfect, definitely improvable, but I disagree with a lot of the common complaints people have with it. This class is supposed to be an introduction to the game and while they can definitely be improved I think they did a decent job implementing their base idea.
Imagine if the Shooter class were simplified a bit more. You technically could get rid of "fluff" and end up with a lineup like the four Splattershot main weapons, .52 Gal, and Jet Squelcher. Other classes have like six main weapons to represent them tops so let's go with these.
Now picture someone who's newer to the game. They're not super great at aiming yet, but really don't mind because they play Splattershot Jr. and getting closer to people like you need to with it makes the job easier. However, they really don't like how bad it is at fighting and might not mind giving up some of the other strengths of the weapon if it means getting better fighting. You could tell them to pick up the Tri-Slosher but there are A LOT of differences that could pile on between the two weapons like the paint output being worse, the fire rate technically making each shot way more committal, and so on.
You could tell them to just pick up the Splattershot and wouldn't be wrong in that but it's not quite the same as picking up the Sploosh-o-Matic would right now. Having a lot of different kinds of Shooters lets people pinpoint the exact things they want out of a main weapon much easier. You could point out a handful of qualities you like in a weapon and start branching out to other classes you find interesting once your mechanics are a bit better.
Not even to mention the kits. I think it's nice to give Shooters as a class access to as many specials as possible just to give people some easier way of trying each of them, whether those people are new to the game or primarily play other weapons. If they were to try and spread out every special in Splatoon 3 across six Shooters with, just to be optimistic, three kits each, they still wouldn't be able to cover everything. That's completely ignoring making these kits synergistic as well, and the fact that someone may be interested in trying to use Big Bubbler without having to deal with something with zero range like the Jr. Look at what we have now though! There are only three specials in the game that aren't on some kind of shooter and two of those have somewhat obvious reasons for not being on a weapon yet. Many of them are even on two! Isn't that nice?
The solution to the above is simply to make more Shooters, but you can't really make too many of them super crazy without the class as a whole having a muddier identity that doesn't quite fit the "easy introduction to the game" bill that it's supposed to. But a lot of them are going to end up being similar because of how simple the class is without making their stats really weird. The problem with making them similar is...well, technically nothing. I think the common opinion is that things like N-Zap and Aerospray shouldn't exist because other Shooters fill similar enough roles to them already. After everything I just said I think they have a good enough case to exist.
Something I've heard from a few people is that other weapon variations should be added with similar properties to one another but different kits. Think the Rapid Blasters. I'd totally be down to see more stuff like that, but they really shouldn't be as commonplace as they are with Shooters. If every class had as many smaller variations as this one then the game would be massively bloated and it'd be a bit daunting for newer players to have to learn. If you want to add a Splat Brella with slightly better damage and slightly worse shielding, a Slosher with a slightly worse fire rate but slightly better painting, and two brand new kits for each, then nothing's stopping you as long as it's not everywhere.
The flexibility is very nice for a newer player to at least feel capable no matter what they feel like they need to try and do. If they want to try and fight someone then most Shooters' kill times aren't half bad, if they want to go somewhere else then their great fire rate helps with that, and if they want to support their team then they can just focus on painting. Playing supportively is a lot more than JUST painting but giving people an obvious and easy-to-perform avenue to do this is nice and it probably works fine enough at a lower level until people take the time to understand the nuance of it and how to improve at the playstyle.
This whole package though means that Shooters are EXTREMELY LIKELY to become meta at any given point. The fact that they have so many more kits than other weapon classes means that it's way easier for them to accidentally land on stuff that happens to be really strong. Compare other classes that currently have to roll the dice for more than a few even decent kits, let alone really good ones, and compare that to Shooters which are already very solid main weapons across the board and also will have several with strong kits. Shooters can always play for their special because a vast majority of them paint well and there's almost always at least one that has whatever specials end up being meta. A weapon or class having more tools to typically push them into being meta is not necessarily a bad thing in most cases but I really don't like it for Shooters in their current state.
This part isn't exactly a hot take but Shooters being the easiest class in the game and always being meta-relevant leaves a very easy gateway for people to just not try and learn all of the other cool weapons in this game. Imagine someone plying the game for the first time, getting the Splattershot, and hearing from a friend that it's one of the absolute best weapons in the game. "Okay. Cool. I think it's fun, so I'll just keep playing it then." And then this person goes on to only really play other weapons once or twice, not really enjoy any of them as much because they didn't click the same way as the Splattershot did because it's easier, and then end it off there.
Shooters as a class should not be doomed to being low tiers but I think any of them being top tiers at all is something that should not happen. High tier is fine for them so people can play the weapon they like at the start of the game knowing that it'll be relevant, but giving them even the smallest amount of incentive to pick up other stuff in the actual top tier weapons. This is where I think Nintendo kind of failed even if there's no great solution to it.
The unfortunate thing is that Shooters are some of the only weapons in the game with consistently super good painting and just removing them from the game might constrain team comps a bunch. You NEED good painting to have a good team comp and not having Shooters would make it harder to tick all of the boxes that a good team comp needs. I think a good place to start would be just giving minor buffs to every other weapon and major buffs to low tiers, plus maybe making Brellas and or something have a crazy good paint output since they're clearly designed to be supportive and could use a big boost like that. Shooters as main weapons need to feel slightly weaker than they currently to by comparison just to compensate for how they're basically guaranteed to have stronger, more synergistic kits in one form or another and the balancing team doesn't seem to have realized this.
Sooo, yeah. I spent two and a half hours writing this. Anyways, even as someone who defends this class I think it still has problems. Take it more as nitpicks to something I think is currently in a good spot right now. I just think people are way too harsh on this class because there's been way too many points where they've been way too strong. I don't think the class's core design is super flawed, but their problems have pushed them in a way that make them really easy to find problems with for one reason or another. I promise this isn't out of Shooter player bias either because I've spent my last five months with this game playing like 80% one of the Stamper kits, it's by far my favorite weapon at this point and I wish it had Tacticooler solely so I could play it even more to fill out teams better LOL