Fox isn't 50:50 with MK or that close to it lol.
Also Fox cannot consistently escape tornado. Escaping tornado is much more complicated than just "SDI/Footstool/other thing that is guaranteed". You have to factor in what MK does/where he hits you/when in the animation he reaches you. Can Fox escape everytime if MK doesn't rise with tornado/keep pressing B? Can he escape if MK only hits him with the very side? What makes Fox/other characters pop out of tornado? Does weight/floatiness factor into it, and if so, what effects do they have? Do you know the definite answer to these? If you escape from Tornado, can Dair break through the sides? Can you footstool the corners of MK's Tornado?
As for the matchup, MK turns it more into his favor with SDI+Tech of Usmash. Call me crazy, but doing this consistently saves MK HARD in this matchup. Grab release to Usmash? Nope, it won't kill if MK SDI's and Tech's it. Not only that, but he can then Dsmash you and you can't SDI and tech that Back lol. If he Fair's your shield incorrectly and you Usmash OOS, he can SDI down and tech and punish. This aspect of the matchup makes it much harder to kill MK, especially since that's not only Fox's choice move to use to kill, but the only one with realistic opportunities to kill with.