Unless you get them from behind, you will lose in close combat to tacs or devs if you are using the chainsword.
The reason? Tac roll is faster and covers more distance than your jump pack dash, your dash attack doesn't stun, your "death from above" doesn't stun, and your chainsword takes almost twice as long to kill a dev as a dev takes to kill you point-blank with a heavy bolter.
It is too easy to kite ASM as tacs point-blank. Even with the basic bolter, asm are at a major disadvantage point blank with the chainsword because 1. they attack too slowly and it's much harder to land melee hits than it is to hold the reticule over the asm and hold the trigger down; 2. ASM vs Devs is suicide if the Dev has stomp, since he just stuns you after you jump/bomb him, and then guns you down in .3 seconds, and 3. tacs can easily just roll and kite, shooting all the while.
To balance ASM they need 1. more speed, especially on the dash attack. You should not be able to just walk away from an ASM once he is within arm's reach. They trade firepower for speed and melee, make the jump pack mean something when dashing/chasing after an enemy.
2. Make the ASM's dash/charge attack and "death from above" deal a stun for a couple seconds like the Dev's stomp. Dev stomp is currently the best melee attack in the game: a stun that actually works (the other "Y" attacks don't seem to be stunning the opponent, unless you chain 4 hits together and do the double stomp. What is it with foot stomps? Why not some kind of weapon attack?)
3. Make ASM immune to the stun of non-assault classes, especially Devastators. Devs should in no way be at a huge advantage in melee, and they are right now.
4. And most importantly of all - make the "X" attacks interrupt shooting, so the victim of the chainsword/power axe cannot just stand there and gun you down WHILE you wail on his face. If he can roll/dodge/ get out of the way, then fine, but point blank he has no business "not flinching" when getting hit with a fucking chainsword, and no business "not getting stunned" when hit with XY or XXY attacks.
5. It would be nice to have a lock-on feature of some type so ASM can chase enemies. If they roll to the side it takes too long to reposition the camera, and it's annoying to hack at an enemy unseen because he is "below" your field of view. Either that, or allow us to zoom out more so we can see what we're hacking at.
Playing as tacs and devs is fun, but ASM are seriously lacking and the thing they need most is melee power. They cannot match guns at all, ESPECIALLY up close. Guns are better melee weapons than melee weapons, and that is just wrong.
TLDR version: Add a flinch/impact firing interrupt to the melee weapons' "X" attacks that makes it impossible to hose them down WHILE you are directly under attack from melee weapons, make stun attacks actually stun, make charge attacks worth something, and take the stupid stomp stun away from Devs - or at least make it NOT work on ASM's.
The best close range weapon for DPS in the game right now is the heavy bolter, followed closely by the melta gun and then the storm bolter. Chainswords would be way at the end after bolters (you can actually out-dps the chainsword with the bolt pistol if your aim is good). Does not compute.