If your going by statistics, then your forgotting the evasion and accuracy stats. Zell has far superior accuracy than Tidus's evasion. So, no matter how fast Tidus is in speed, most likely, Zell will still be able to connect attacks. And Zell's defense and attack power is better than Tidus. It will take Tidus longer to take Zell down. And, let's not forget the fact that Zell can use any magic due to FF8's draw system. He could use Haste and Meltdown, and Meteor, magic FFX doesn't have.