I think Tizoc is very viable, he has alot of really good pokes in my opinion, and even with the throw bug, it's not like he can't still use tick throw setups to be offensive and mix it up. It's just when Tizoc is on the defensive, his punishment tools are really lackluster compared to anybody else. Being able to Just Defend and Guard Cancel consistently are probably requirements to make the most of Tizoc. Plus his damage is insanely good when he nets it.
As for Kevin, reason why he's so top... he can build meter extremely quickly, he can chain multiple DM's together, his break move hits low and is very safe, if he scores any random counter hit, that's easily half a life bar or more, he's got good evasive moves, his normals are all very strong. Everything about him is good.
I'll admit though, it is kinda rare that I ever see high level gameplay from Kevin in most tournaments, I see way more Gato, Jenet or the Kim Bros.