I use him as a backfield striker. With his rifle, he can respectably poke from range. With a lot of recoil reduction, he can crit from those ranges, and put on some serious hurt. I close in, only when I want the kill. If I see someone asleep or out of position, I get close, pop my grenades that slow and burn, and burst the down. If it’s someone hard to kill, I’ll pop Scrap Cannon first, for a little extra damage on my shots. I save his ult, for when someone is either trying to kill me or another teammate. rig it at 10th level to go right through shields, and no one will suspect they’re dying…well, till they’re dead. 
The difference between him and OM, is that OM can’t trade. He can’t sit there and slug it out with someone to push them onto the backfoot. If he gets the jump on them, OM can secure the kill usually. But if he GETS jumped, he has to stealth out or hope for a trick play or external reversal. Whiskey CAN stay in, and force the reversals himself. Tag someone with scrap cannon, bump your assault rifle damage up and they’ll generally beat feet long before you do. And that’s when you hit them with the nades in the nads, and drop em. 