I agree with the stuff Eevee said, learn the timing to tech warlock choke or whatever it's called. I don't think teching it actually guarantees your safety, but the option is necessary if you want to not die. Kirby dies so easily in this matchup. And the tech timing for this move always seemed strange to me.
RIP Kirby when using Final Cutter, Upper Cutter is so necessary ;_;
Playing against Ganon shows what the core of the game (and any fighting game) is truly about: don't do anything dumb and get hit. Ganondorf has a few terrifyingly fast and strong disjointed moves, like Dtilt and Upair, but overall he's slow and you should be able to react to just about anything he does. When you were at high % first game, and had taken the first stock, you should have camped your butt off. This is probably true in most matchups, but especially someone as slow as Ganondorf: if you have the stock lead, try not to approach, and rack up as much damage as you can before you lose your stock. If you're like me, you like going aggressive, but it's a bad idea when Ganondorf can make one read and kill you with an Upair that easily beats ALL of your aerials.
Good job respecting the Ganoncide when he was offstage, that's a sad way to lose. You shouldn't have given up though, it was still very winnable. Take his stock and get some uptilt combos, force him offstage and gimp him, it's possible.