I think that the differentiating factor between Painbrush being allowed to be threatening and it being forced to play passive is the ability to paint it's feet quickly. You can see this difference very clearly between both of its kits. Curling Bomb fixes so many holes that Painbrush has, some that you didn't even realize the weapon had to begin with. It also means that a very limited amount of subs work for it. Most bombs don't work super well for it because they don't paint it's feet fast enough. Chip damage bombs like Burst and Fizzy paint it's feet but Painbrush doesn't benefit from them as much because it can't combo off of them super effectively. Which is where Sprinkler comes in.
Painbrush is a very strong weapon when it comes to burst paint, but it can struggle to paint more consistently because of how slow it can be. Sprinkler fixes that problem, and allows Painbrush to paint walls easily, another issue both kits struggled with. Another thing Sprinkler does it it gives Painbrush a buffer, either to escape from a sticky situation, or the ability set up it's swing from a more aggressive position while the sprinkler tanks hits for it. Not only would Sprinkler help Painbrush with it's weaknesses, but also bring out more of it's strengths. One of Painbrush's biggest strengths, especially the vanilla kit, is the ability to take a key part of the map and be impossible to remove. Sprinkler allows Painbrush to take control of that area quickly, by setting up paint in that zone faster, AND it lets Painbrush defend itself from people trying to take that area by giving it armor to work with in a fight.
Kraken is much the same. Painbrush is a slow weapon, so one of the best ways to beat it is to just run at it with a shooter and dare it to respond. Well now Painbrush can just pop Kraken and turn the tables in an instant. Especially when Painbrush is holding down an area like it usually does, Kraken can offer Painbrush an escape route if things get hairy, or the perfect enforcer to defend that position and scare people into respecting it. Kraken even helps Painbrush get into those strong positions to begin with, and then it can use Sprinkler to defend itself once the Kraken runs out.
For the record, I don't think Painbrush will ever be good. But I like it that way. I love Painbrush because of the self-expression and creativity it enables. I like that it has unique strengths that no other weapon has, while also constantly encouraging you to solve problems in order to be effective rather than complain about them. Painbrush is my baby. I wouldn't have it any other way.
