I think both dps specs in regards to PVP are much better off then you give them credit. leth when played correctly loses in damg only to snipers and smashers. leth also can create tons of advantage by dotting up 2-4 targets at once to to give your smashers options for kills.
the issues i find that need to be addressed
1. dots breaking CC... id like either our talent make it so all CC isnt broken by out leth dots or give us something to "recall" our dots and perhaps gain a small energy gain or something.
2. conc needs a better energy flow. this can be resolved simply by looking at the costs of the attacks.
3. hidden strike usable during sneak or auto crit has to happen. or just improve the system for getting out of combat.
4. also expl probe usable by conc not crouched would be pretty nice.
we could def use some work but i do think a good player will always be able to make the specs work fine.