The inkbrush will unfortunately always stay in a bad position. This is thanks to it's awful range, and just pitiful 5 flick kill that makes the opponent feel tickled instead of threatened. While it sure is fast, and it can cover turf, many other weapons can do the same, with workable range + respectable combat abilities, and a better support kit as well.
Weapons like: the Splattershot Jr. , the Sploosh-o-matic, the splash-o-matic, the N-Zap (obviously), and even the aerospray can do what the inkbrush is supposed to do much more effectively. As they can all cover turf just as fast, or faster, and help their team doing so. The splattershot jr and the N-Zap cover just as much turf and they can support their team with their specials. Which is what the inkbrush is supposed to be anyway, a support weapon. The splash-o-matic and sploosh cover just as much turf and their combat abilities are much better with their range and superior firepower. Finally, the aerospray replaces the inkbrush as a special spammer, being able to grab it's specials faster than the inkbrush and being much better in combat as well. Even though the aerospray was a pathetic combat weapon to begin with.
And all this is not even considering that the Octobrush directly counters the inkbrush in every combat scenario, and it actually can kill people without having a teammate close by to it. The only sacrifice you make for using an octobrush over an inkbrush is a reduction in speed, but even then, the octobrush still moves fast and can still cover turf respectably well. Making the inkbrush a weapon that's hard to use, and is unrewarding since it's role on a team can be so easily replaced.