i see them as fairly similar. kicking characters and all. zack has more speed but rig has more power which allows him to beat Zack out with quite a few moves. rig seems to have a bit more tools from what i see. ive spent some time fighting a few rig players and they'll be shocked at what zack is able to get away with against them.
i was really talking about the frames of their moves against each other. but zack even though he is fast takes patience. his sway and duck lead into really good moves BUT on block leave him open to be poked. got to be prepared to cancel accordingly. he needs to be close to be truly effective. i love guard breaks he doesnt have many good ones. but i lovem
if your opponent is slack with blocks and hold they are in for trouble though lol check out my youtube can see some of my zack. victories and blunders.
Zack & Rig both need to be close to be incredibly dangerous but they can get in or fight at range fine. Rig has the general problem that TKD related fighters have of overreliance on highs for pressure. Sarah has the same weakness. Zack's speed + mix-ups/resets make him an absolute beast when on offense. Having an i11 mid allows him to get on the offense fairly easily too with nasty CH's.
He's a lot more similar to Jann Lee than Rig actually, i10 jab, i11 mid, -1 i13 low, its all there, their tools may be the same but their core gameplan is a lot different from each other, Zack is an absolute monster up close but he aches when it comes to spacing, in which Lee is good at.