I empathize with this way too much. The #1 player in my scene was a Snake (until he moved a few weeks ago and we all celebrated :P).
Your pain points
It sounds like you have 2 pain points in particular that you find difficult:
Recovering back to ledge/stage
Snake's side-special, Nikita (which we jokingly call "Taquito"), makes this near impossible, as you've noted. This is a situation where a good Snake has an extreme advantage in most matchups, so you're not alone here!
To counter this, there are 3 options I think you can use effectively depending on where you get knocked off-stage:
If you got hit low, try to either hug the wall as you're coming back up or go a little under stage if there is no wall. The Taquito covers away from stage very effectively, but it has a harder time if you're right below the snake (and even if he does somehow turn it all the way around, you'll only be in a tech situation, not dead).
If you get hit just a little off-stage, instead of drop and recovering, try to jump and immediately air-dodge into the ledge. If the Snake goes for an immediate Taquito, the air-dodge should put you through it and if not, you'll be on the ledge as fast as possible.
This one is Ganon specific, but if you get knocked high and away from stage, you're in the worst possible position for yourself. This is where Taquito is at its strongest. I'd suggest an immediate down-special (warlock kick) to get you low and then use one of the first two bullets.
Getting back to neutral from ledge
It sounds like you're having trouble with some of Snake's tools punishing you for getting off of ledge. This isn't something I've really experienced with our Snake, so I can't give you any tried and true advice. However, I'd find a willing friend to go into training mode with you and spam up-smash so you can try:
Jump-getup into an immediate neutral-airdodge. This one is going to take some timing to get down, but you should be able to get through and up-smash with the air-dodge and safely make it back to center stage.
This is Incineroar specific, but since neutral-special (Lariat) gives you invulnerable frames, maybe you could do a jump-getup into an immediate neutral-special to tank the up-smash and hit the snake? I know specials come out pretty dang fast after a jump getup and since Lariat cancels Incineroar's momentum this will probably let you act faster than neutral-getup into Lariat.
Again, I haven't tested either of these, so I can't promise they'll work, but they'd be the first things I'd experiment with.
So what's the game plan
Notice that both of your pain points occur when you've been knocked off-stage (I'm guessing you're not hopping onto ledge by yourself). So a big part of your game plan with Snake should be staying on stage. How can you accomplish this?
Play safe and slow. This doesn't mean to wait on your side of stage for the Snake to take his time approaching you. On the contrary. You want to be right up in his face--but not so close that it's dangerous. You want to strike the perfect balance of being close enough to punish if he starts pulling out grenades/C4 or does something punishable, but not so close that he can hit you immediately. This will keep the pressure on them and ideally suffocate their neutral without you over-committing and being hit off-stage.
For more on this, I'd suggest watching this match between Ally's Snake and a Ganon. Watch how the Ganon tries to stay within a Nair2-foot-length of the Snake at all times, since that's one of Ganon's safe and fast moves. You can also look for more competitive matches to see how the pros deal with this matchup.
An aside on GSP
You can use this site to get a pretty good read on where the Elite GSP currently is and what that means for your standing, but in general I wouldn't put a lot of stock in GSP.
There have been countless posts about how finicky it can be. Not to mention that my roster avg right now is around 4 million, so if I pickup a character I've never played before and win one match I'm suddenly in Elite with them.
Honestly I'd ignore the GSP if you can. Play online to have fun and learn matchups. Rematch if you can to try to get a more realistic competitive/tournament feel.
In general unless you're someone who can't get a GSP over 2-3 million right now, the number really doesn't say a lot about your skill level.