The Striker is Platinum-Viable. Here's what you'll need:
Striker
AR Extended Barrel
AR Expanded Magazine
Incendiary Rounds of your choosing
Rifle upgrade consumables
Stabilization Module Consumable or Barrage Upgrade Gear (use Warfighter Pack if you're using the Consumable)
Human Soldier level 20 with Adrenaline Rush and Grenades
Start firing your Striker at your opponents. When you get to about 3-2 rounds in the mag, fire off Adrenaline Rush. Enjoy a full mag of the maxed-out fire-rate and several glorious seconds of massive damage. Once your barrage ends, hit the target with a Frag Grenade to cause a fire explosion. Laugh your ass off when you outscore the N7 Destroyer on your team and rub it in his smug ****** face. BOOM! Fun for the whole family.
Plus it uses Human Soldier, which nobody uses and wins at everything forever. Do note, however, that it chews through ammo at a solid rate - familiarize yourself with the ammo crate locations, because you're going to need them, and Thermal Clip Packs if these prove insufficient.