For me, the tools that have worked better against Fireteams are: - Gao-Rael + Smoke or - Sukeul HMG + Nimbus (or White Noise against visors). You spend half of your turn slicing the pie and killing members (if there is more than one visible), but you reduce the order pool and one of the most powerful attack/deffense piece of the enemy. And if the enemy is dumb enought to bring too close his Fireteam, Symbiobombs can work wonders.
Only reason I don't like smoke+msv2 is that although the rest of the members cannot shoot back the visible target will still be at max modifiers.
That's why, if possible, you start shooting to the less dangerous guy (NOT the Missile Launcher or the Multi Sniper), while keeping your Symbiomate close: 2 wounds + Symbiomate + more dice (three for sniper, five for spitfire/hmg) means that statistically the combo will work.
Just gotta watch out for core link teams. SSL2 can best our Gao Rael. Sometimes you're better off shooting with the Sukeul HMG or getting close and firing a VCR with tapes.
