I fought a pretty good Little Mac player and jotted down some notes for the matchup:
-Your Jab is key. It's fast, it can get him out of your face, and it can beat out a few of his approach options.
-Always charge Thunder. It's frustrating since Mac is always gunning for you, but charge it whenever you can; it'll come in hand when it comes down to KOing him.
-Short hop Arc fire is useful for locking down his movement options at mid range. Mac doesn't really do air, so his only method of approaching you is from the ground.
-He can punish you pretty hard up close, so throwing out unsafe options (such as smashes) is a serious no-no. LS Down smash is somewhat acceptable to cover rolls, but that's it.
-The roll cancel grab is immensely helpful for grab punishing him. It's not the end of the world if you can't do it, but it's really helpful (if you land a backthrow at mid %, you can dish out heavy damage or potentially take out a stock)
-Always chase him down in the air, but be careful Edge-guarding him isn't as easy on practice. He's capable of covering himself with his counter, which propels him forward if activated (and if not, he's at a position where he can grab the ledge) this is why Thunder is useful, since it bypasses it altogether. That said, if you get a good read and land a LS aerial, it's lights out. There are some cases where Nair is more useful at edge-guarding due to its superior speed.
It can be a frustrating matchup, but it's certainly doable. You just have to keep a cool head and play even more patiently than normal.
I'll get to actually talking about some of the points you bring up, but I'm going to go right ahead and say I've yet to find anything that even felt CLOSE to 65-35 or worse.
I'd be careful about throwing around numbers like that, especially this early. You have to remember, 7-3 to most people essentially means 'Super hard counter', which I don't think is even close to the case.
They are difficult match-ups, to be sure, but I've yet to feel like there's anything worse than 4-6 for Robin. Only exception would be Mac/Sheik/Greninja on Final Destination SPECIFICALLY. That stage makes all of the problems in those match-ups worse.
I will be using my personal ban on Final D 9 times out of 10, I think it's easily one of our worst stages, especially against those 3.
I feel the same way. There's always a path to victory with Robin, you just have to be patient and find it.