Everyone talks about his disadvantage, and although buffing his recovery and air speed would be nice, that's not all he needs.
His advantage state is horrid as well. For all the work it takes to get in, he just isn't rewarded enough to compensate the struggle. Here's what I would do to change that:
1) Give Ganondorf a kill throw
There is literally no reason to grab someone after 100%. Why shouldn't Ganondorf get rewarded for getting in and actually grabbing the opponent? Right now, all Ganon can do after getting in is get like, a two hit combo and return to neutral. At death percent, Ganon relies on random hits just to kill someone. That by nature is inconsistent. Why not give Ganondorf's power a purpose past 100%?
2) Make dtilt a combo starter, like Melee
His attacks launch too far away to do any substantial combos. What's the point of approaching if you can only convert it to something below 30%? The loss of his old usmash not only hurts his speed even more, but also removed combos for a big, strong attack, of which he has plenty of. Making dtilt a combo starter would help his god awful netral better, and would make approaching him a bit riskier.
3) Make side-b untechable
Side-b is such a pointless, bad move. It only combos IF your opponent doesn't tech. 90% of the time, its a waste of time. Bowser, Incineroar and Ridley all get great damage and win neutral just by landing it. For Ganon however, to make it useful, he must make a successful read or pray they don't tech. Making the move untechable, along with making dtilt a combo starter, gives Ganon a good combo string (side b, dtilt, nair, uair, etc idk) and an actual reason to approach outside of stray random hits.
4) Give Ganon a kill confirm
Probably wishful thinking, but a reliable way to actually kill would be nice. If flame choke is untechable, making dtilt kill would be nice. Or, maybe make dtilt>fair or up air true at a certain percent. You may say that sounds broken, but do remember that Ganondorf is still a slow punching bag that dies at 40% off stage.