Gameplay changes have taken a backseat for too long now, I think. I've been playing Reflex since it came out and could ignore some shitty balance because I like the game, but I actually have to stop playing now -- its getting too frustrating. I understand that the team is small and they'd rather work on more exciting features like cosmetics, matchmaking and whatnot, but gameplay changes have to happen at some point...
I think changing the knockback system is the place to start. Making small changes to damage or splash radius won't matter until its fixed. Rocket pops make fights so unpredictable and really encourages bad play. I've found that most people out of control, even high level players, won't make any tactical plan to get back control, but will simply pickup the nearest rocket launcher and dive on you hoping to get a good pop (I'm being a bit reductive to make a point). And some people have good enough rocket aim that this will work consistently for them. The small splash radius exaggerates this problem; moderate differences in rocket aim result in a great difference in the number of rocket pops.
Lowering the ammo quantity would probably be enough for bolt, and maybe for ion cannon (although it will probably need some knockback tweaks too). With knockback and splash changes grenades would only need to be slightly shrunken; overall, I like that they are powerful. Plasma and shotgun seem good now (I did like the slower plasma though), and burst needs to be buffed.
P.S. I should clarify, the problem with rocket pops isn't that you get bounced, but that it only ever sends you straight up, making you a pathetically easy target.