After playing with him for 3 seasons I'll give you my full opinion.
So, as a pocket, Brimstone has monster DM, crisp rockets, creates a ton of space for his team, maincalls, usually takes low heals, and was always the most eager person to play the game. Seldom missed a scrim if he could control it, scheduled and organized so we scrimmed more, always found a ringer or a last minute scrim, if we ever had dead time or were still energized afterward we'd go right into a demo review or DM or MGE for hours, never left Mumble until long after we talked about our issues. When he started to struggle last season he immediately went looking for a mentor.
That being said, Brimstone plays very aggressive all the time, on top of playing on low heals. Sometimes he'll drop into a group of people and get three kills, but most the time he'll end up feeding. He tends to rush things a lot, tends fill in other people's roles if he thinks someone isn't doing it effectively, and usually that means forgoing the role of pocket and being a second Roamer. Those things are manageable and can work with the right team that can play at his tempo, and it's possible to reel him back in and play Pocket again, but the worst part is this usually leads to him tilting, and Brimstone is a very vocal tilter, and rushes even more and dies more frequently. (He's also pretty cringe with memes).
He's still a great friend and was a part of why ESD succeeded as long as it did, and he can only get better. Pick him up, he's a Pocket (or Roamer) who does whatever it takes to get better at the game. Plus he's spent the last two seasons in ESEA maincalling.