I found that setting up long range "reaction fire trap" with lasers will keep enemies pinned down with minimal threat from plasma weapons while your close assault guys flank em.
I found plasma weaponry quite...well, lacking something. At extreme ranges, lasers rule. on longer medium ranges, machineguns work better for more dakka approach, then, grenade launchers are kings, and on close combat, flamers and plasma blades. The only plasma weapon besides blade that found use in my arsenal is pistol, as secondary weapon for laser troops.