That’s the name of the game. Effective use of cooldowns. You’re a rogue, you are meant to pick your fights, that’s why you have stealth. If you feel like you can’t kill your target off quick then just leave. You have blind you have gouge, Cheap Shot,/Kidney, Disarm, Smoke Bomb, you name it.
Shadowmeld causes you to leave combat which lets you re-stealth, so yeah when timed and executed right, it is de facto an extra Vanish.
I levelled a rogue to 80 and got destroyed on packs of 2-3 mobs. I watched guides but I still never understood what I was doing wrong