Well, they’re giving you the corner, and then you’re doing something rash out of frustration as soon as you catch up to pounce on them and they’re using it as an opportunity to jump over you, I guess. The answer is probably just to be patient, bulldog (i.e. move forward, block) your way forward through the fireball spam, and then laugh at them as you abuse the corner advantage. If someone tries this strategy in the Jago mirror then they’re probably just going to end up cornered and blocking a lot of HP xx fireball into overhead and other unpleasant stuff, and eating a DP if they try to jump out. As for Shago, I guess he can get out more easily, but he still has to take a risk (story of Shago’s life, really), and most characters can probably keep him grounded with normal pressure anyway, so being in that corner is still unpleasant.
On the other hand, if you’re TJ and I’m Jago, I’m rarely if ever going to throw fireballs at you in the first place. You’ve got two options – powerline and tumble, hell maybe a third given how quickly flying knee crosses the screen – which completely wreck a Jago trying to zone out a TJ, and you can also knock me down with the blast wave off tremor from a screen away. Basically, TJ more-or-less wins the neutral game against Jago and just has to worry if he gets put on his back by a DP or something.