Old timer needs some advice

[Belfort 0]

Hi

I am in a bit of a tight spot at the moment, I really struggle to understand/learn the current assassination spec. I know i'm doing something wrong, as reading on the forums ass is god-like, insane damage and shit. The thing is i get blown to pieces by quite a few classes. 1 stun and i'm gone. Outside evasion almost all melee classes are instant detonation. Maybe with the except of other rogues. 
Take the DH,
I get 100-0 in the AOE stun. It goes through evasion and cloak. I realize that it's a rock -paper- thingy but most of their damage seems unavoidable. Outside evasion i'm dead. I've tried everything, I can bring them down to 10-20% and "puff" they are back to 80% health. The evasion is used to survive the first 8 secs. If not popped i'll instantly die. 
They seem to clear DOTS randomly, they have some kind of evasion so landing the full kidney-shot misses a lot. Their ranged attack hits 8-9 times harder than mine, so kiting their burst is impossible. Vanishing is impossible, as i can be spotted instantly and my stun DR's are already up.

Almost all classes just use trinket on the cheap shot and they don't seemed to be "punished" for at all! there is no consequence like there used be.

The stealth seems to break out of frekin nowhere, latency is now working to the laggers advantage, as in, unless i'm 1m ahead of the target my stuns wont landl, i just end up doing a stupid animation!

If we ignore the mandatory l2p, I would appreciate some advice!

I played since vanilla and got my shoulders and all that, I know my way around a handful of classes. This expansions pvp “balance” or complete lack of, just seems odd.