I've played with my sin to plat and destroyers are my favorite match-up, pretty much win 100% of the time.
All you have to do is sit in stealth and wait their spins out. You can also time your boltstrike to hit when their spin runs out. You can body swap them in their spin and stun them after shadow dash, Q the inevitable tab to restealth, land the throwing dagger and wait for spin downtime to daze into knockup and go ham.
You just need to maximize on their trinket downtimes, that's all. They're really easy to beat if you know what you're doing. My advice is just look up some guides about sin pvp and keep on playing.
And if you're trying to RMB+F them, you're doing it wrong.