The game isn't even that difficult up until the 70-star mark.
I mean, there are a lot of people who think SMG2 is piss easy, and that flabbergasts me, but there's no way that the game surpasses "medium" difficulty (at most) when you're just going through it in order to fight Bowser and be done with it.
Besides, the "?" stars aren't a sign of difficulty if they're just the ones where you have to feed hungry Lumas. That's because these Lumas aren't really hidden at all, they're in plain sight. The challenge, I guess, comes from finding the right amount of coins/star bits to feed them, but it's never really that bad.
Nintendo didn't "flip the script" entirely, here. They made getting the full 100% harder for the more dedicated gamers, but that's just a nice little courtesy to those who felt that SMG was easy more often than it needed to be. The baseline 71 star quest, as I see it, is no harder than it was in SMG1, and even then there's at least the Cosmic Guide to pick up the slack.
Really, you're in the final stretch. Just step it up for this last 6 stars. Be patienct. I have faith in you.