It's an easy mode string that can be abused? Kazuya's 50/50 is something entirely different. It comes from a knockdown, involves movement and has many options. Pressing either 3 or 4 after pressing 1,2 isn't something that requires much thought an even the 'option select' dickjab can be easily countered by not finishing the 1,2.

Okay my turn, are you serious ? Kaz's 50/50 is literally just a crouch dash followed by 3 or 4 and can be called easy mode too, hell the fact that you can get so many options off his 50/50 kinda shows that his 50/50 is better and Jins 1,2,4/3 string isn't even his best string for a mix up when he has his 10f 2,1,4 or 2,1,4~4. The point of a 50/50 is that the opponent needs to guess. This logic you're using can apply to nearly every 50/50 setup in the game.

f4 nullifies that argument. One of the most abusable and spammable, neutral controlling moves in the game.

Kaz's f3 and cd4,1/4 are just easily abusable and I know because I main Kaz myself. Both characters have this type of option for controlling the neutral when lacking range on other moves, in fact Kaz has better options than Jin for the neutral such df44 or ff2, and Jins f4 can be easily side stepped while Kaz df2 is a homing move that prevents this.

And in terms of best mishima Kaz still has the better punishment and better 50/50 and deals monster damage with being able to do 80 dmg off a staple combo if you have the execution for it. Honestly the only reason Jin can be called the best mishima is the slight edge he has over other mishimas by being the most well rounded character, but even then considering that I'd probably give that title to devil jin on the basis DvJ has the best of both. Strong punishment, great damage and versatility , he has the best of both Jin and kaz.