Competent player > Incompetent player.
I've seen some stacked PUGs on my server, so it all depends on who's running with who and the level of communication. Hell, we'll run premades of 4 different guilds and it'll look like a pug, but we dominate.
Mercs are support role class, people aren't playing them correctly. In good hands like yours, they can be absolutely devastating and Pyro Mercs are very viable. I have a guildie who runs it and he tops the DPS charts as well.
Arsenal has it's own issues, but I've seen Arsenal players do extremely well. The problem is that they think that they should act like a rotating turret. It needs to be a TM TM TM, move, railshot on the go, Proc'd Unload. The more mobile you can make yourself, the more effective you become. Hug corners. Little things like that.
i dont understand these people... did you actually play a merc? its horrible, powertech is better in assault spec, better then anything merc can bring. arsenal is to easily shutdown, even a recruit gear sentinel can annihalte you not so hard, and assault is simply not reliable.