Well, try playing Plunder or Team Objective so you can refine your skills and you don't need kills to win. Once you've gotten better, try going into TDM. If I were you, whenever you play with a REALLY good player, add him. Then you can party up and win. It gets better, I was once in your position. But now I'm pretty good. Just keep trying and stick to my advice.
It's really difficult to win against Legacy 5 players but the only way to get better its practice. Here are some advices
Aiming its better than blindfire shooting. Practice your aiming.
Many player have revenge as booster. Be careful when you kill enemies with punch or stealth.
Try to get treasure chest to activate medal kickback quickly.
If you can get power weapons like hammer or rpg, try to use them but be careful, you can kill your partners and get expelled from the game.
Try to get cover while shooting, but don't stay in a single place for too long.
Use booster like Fleet Foot to move faster while aiming and Revenge to drop grenades after death.
Thats what i did and now im really good at multiplayer. You'll get better, just practice.
Yeah I know I don't like to use revenge either, i only give him the advice to help him a little leveling up to buy upgrades on weapons and boosters, i use fleet foot and secure team. But when you are killed because many players are really good, i use revenge cause you got kills, it helps your team, it helps you. Im pretty sure many players use revenge.