in my mind i think the most realistically effective setup is 3 shooter type weapons and a splat roller
2 people with splattershot type weapons on the front line coordinating with each other directly and covering the main area, and the splat roller on the flanks doing most the territory coverage. one player in between the duo and the roller with an versatile role; protect the roller, and come up to the firefight if things get out of hand
splattershots are VERY strong in this game because of their adaptability. since its just 4v4, weapons that are only strong in a niche like chargers aren't going to be very strong because unless your team compensates for that role perfectly, you're effectively turning the game into a 3v4. this is why classes like the sniper and spy aren't picked at all in competitive 6v6 in tf2; they're good classes, sure, but you have better choices that can get the same job done more simply and effectively with this small player count.
rollers are very interesting, probably my favorite weapon, even though i'd never pick it. you sacrifice a lot of mobility (you can't flick ink far enough ahead of you to squid up and save time, or even splatterhop) and range for ink coverage. since it's so close range you don't stand a chance against people directly in front of you; you have to flank them. stay out of their peripheral view and get behind them. that's the safest way to secure a frag. and because it impedes your mobility, you're going to have to rely on your team to make it to choke points before you, where they have better weapons suited for the job. this is where my competitive composition comes into play:
you have a duo with incredible adaptable roles that can take the other team's duo straight on or hunt down their roller user. and since there's 2 people on the front lines constantly spraying ink, and the other team is doing so as well, they always have somewhere to be. being a part of the duo is going to require a lot of skill, since you always have to be in the right place at the right time.
you also have a roller that's protected by a splattershot user that's vaguely close to them, so you have INSANE ink coverage on the flanks. this is probably the player that the duos are going to be hunting the entire game, and what makes up the meta. map control will be monumental in this game. if you shut down the opposing duo and consistently assassinate their roller user, you're denying them so much territory, they can't advance, and they can't win.
so here's the basic formula:
- 2 splatter users on the front, 1 roller user in the back, and 1 splatter user in between with an adaptable role
- the duo up front sprays the front line with ink and searches for the opposing teams roller user
- once they reach that roller user, either the other teams duo will be covering ink up front and it's just the roller user and splatter user, making the fight a 1v2, or its the entire team, making the fight a 3v2
- if its a 3v2, you have to buy time to get your other splatter user to the firefight with you to make it a 3v3
- conversely, if you're in the 1v2 scenario, you have to buy time to get your duo in the firefight to make it a 3v2
- the team that can consistently win these firefights and take down the roller users will have a substantial upper hand, because they're denying so much territory and covering it with their own ink
- teams will wobble back and forth doing this to each other, and the one that has players doing their jobs the best is the winning team, since they have control of the map
you can get really creative with team composition in this game, but with the current information we have alloted, i think this is going to be the most simple and effective one. you can't go wrong with this much adaptability.