I think that the devs need to be willing to change kits post launch. Balance is a very difficult task, and I don't think it's unreasonable that the devs make mistakes during the initial reveal of kits. That's why we have balance patches. Because balance is often a task best performed through trial and error. The fact that the devs are locked into mistakes they made at the beginning of the game makes it more difficult to balance the game and can cause aspects that weren't the primary abusers to get hit by collateral damage.
Sloshing machine was a balanced weapon in previous games, but became broken on launch S3 because it got a kit of fizzy/booyah bomb. In order to finally stop the weapon from being the uncontested best aoe weapon, it needed a big hit to it's firerate that will affect any other kits machine has/will have in this game. It would have been much cleaner if they could have just addressed the source of the problem. Beyond that, kits being static means that any special that turns out bad is going to kill a bunch of kits over the course of the game through no fault of the mean.
I've played games that would swap around secondary abilities between the characters depending on balance. It worked out fine, and the game unquestionably has a better distribution of these abilities now than it did at launch on the base roster. It's overall better for the game if neo sploosh gets something actually useful even if little timmy likes it.
I don't think custom kits is the solution to kit issues like a lot of people think. It would break too many aspects of the game and I honestly feel that variety would go down, not up. But I do think the devs stubbornly refusing to ever change their mind on kits is a problem.
