Focus for Thief
I am all for thief skills that debilitate/hinder opponents. Also sword shouldn’t have the same dual skill as dagger, all skills should be unique.
That said here are some assassin skills from gw1 that could be remade (with similar functionality) for the thief.
Iron Palm
it could be changed to say: remove the blind condition from your target and deal x dmg and cause a 1 sec knock down (no effect unless blind was removed) or something to prevent mindless spam, same thing for the previous skill.
Mark of Insecurity
could be changed so that it end early if the target moves a certain distance from you (say like 400 units or so, something low ranged so that it is easy to remove cos it is spamable) and it could put on a negative regeneration effect that scales with condi dmg, and for the second part of the skill it would make boons expire faster (since that is the equivalent to enchantments)
Siphon Strength
same as Mark of Insecurity- ends early if target moves a certain distance from you, also a high ini cost (like 7 or 9)
Beguiling Haze
again high ini cost and a failure state (like no daze unless your target has no boons or something to make it more timing/combo based rather than just brain dead spam)
There are allot more skills from gw1 that could be remade (but still be made to feel similar) should anet ever make new weapon/utility skills.