I always thought the mechanics behind it cause me the most pain. It can only kill at close range in 4 hits, taking the time of a Dynamo roller, at the range in which every gun becomes even more powerful. I'm yet to have a 1v1 without losing or a suicide kill. Plus I've had entire shots negated by small objects. The saltiest for me was when a cone on Urchin Underpass stopped me from killing the Rainmaker.
I also don't feel too much pain from button mashing. Maybe its because I use my middle finger, and save my index finger for the sprinkler.
I find the main downfall of the inkbrush is that if other players don't exploit the opportunities it can create, it is easily overwhelmed. Basically, it's deadly with good teammates, and dead weight with bad ones. You can try to carry a team with an inkbrush, and I kept taking out a whole B- rank team with the brush and Ninja Squid earlier, but it was pointless cos my teammates kept dying in every firefight. You can only fend four off for so long, and they weren't stupid players. They eventually just pinned me down, and that was the match over..
This is why I'm forced to give it up in ranked. Its bad enough when my teammates don't know how to take advantage of a clear side path I inked directly through the enemy's side and instead charge one at a time into a sniper's FOV, or push up once I eliminated the entire enemy team from a flank. My worst was in B- when I was paired with C+, when a sniper took me out, then jumped right behind my teammates, and just wiped them all out at point blank range, and they never even noticed him. I've had teammates in Turf War who've taken better advantage of what I do than my B teammates, who managed to push up while I've roped the entire enemy team into focusing on killing me. There's a limit to how much we can carry, and in rank we're forced to use kill weapons just to be the least bit supportive. Plus its even more difficult to support sometimes, because they randomly eliminate Miiverse posts that I can usually place a sprinkler on. Still trying to figure out how to get the sprinkler on the center beam in Walleye Warehouse, that would be amazing for Splat Zone.
Plus walking backwards and shooting automatically wins any fight against an Inkbrush, meaning skilled players don't even have to try that hard to kill you. At least the Carbon Roller rewards a sneak attack with a kill every time, where I've actually lost fights without getting the kill when I start attacking from behind. I really hate the damage scaling at close range...