just reading through zul jin's stuff
he's a high dmg auto attacker w/ no mobility and low utility, so with that as his identity he will always be bad unless he's overtuned.
looking at his talents this seems like the build to me:
1. range
4. atspd
7. viscious attacks/recklessness if you are going taz, but even then vicious is good
10. both seem decent, guillotine needs help to land against anyone who knows what they are doing, basically a worse chromie w but still useful on a character like zul
13. movement speed off of q, voodoo shuffle can be good, like his main weakness is cc. forest medicine can be good but the heal amount is low. to me that talent should be baseline on the e.
16. atspd
20. situational, but take amani if you went taz
cant think of a reason to use him over say valla or guldan, unless spell armor really starts to take off
he can probably poop on ppl who don't know how to trade
regeneration is pretty bad, but it saves you from dot deaths