okay time to give my opinion about this
sha is probably better than you think
he has a good mobility yaknow compared to other dmg... cd is a bit long that's true
desert shadow is way better than you might think, with the reset card at 45% health, it allows for a huge burst when facing a flank, can allow 2 shots intead of 3 even on people with extra health cards (these cards will render explosive arrows useless) plus compared to explosive arrows you keep the nice stun possibility
recurve is my go to talent not much to say about it
as for cards
wanderlust is an SSS card, if you don't run it at 4-5 then you don't play sha lin
poise is...meh, if you know when to draw the bow then you don't need this, I mean it's not that useful, it didn't exist before and people never had any issues without it, I've tried it and I find it useless
bullseye is great as you said
extra health is useful kinda
but you lack, the cd reset on withdraw when low health omg, this one is so important, always use it please
other than that it's nice
planted is best used on stunned (and such) enemies or to melt shields, as you said planting in the middle of the map will get you killed, don't overuse planted seriously
withdraw you don't need to save it that much, using it when you fight is great, either to avoid a shot or to finish a kill
there's not much else to say about sha anyway, he's pretty basic