So what about every other point possible from which he might start charging up-b?
This chart is pretty much universal. Yeah, you can absolutely draw more points, but the same principal applies.
What about if he starts charging early enough that he can get onto a platform? This happens a lot, he doesn't have to be above the stage when he starts charging for it to be an option.
So, same principal here. You know he's charged it too long to sweetspot. If you're standing at the right spot to cover all his options, you've got this. Just watch him charge. You know how far he's going to go. You know he can't sweetspot. Just stand there and get ready to jump and whack him if he goes for the platform.
What If, instead of charging farther when he sees you go for an edgehog, he just releases and knocks you away before you edgegrab?
...then you grab the ledge first, and he does.
That's the point of threatening to ledgehog.
He can't up-B before he's charged enough to sweetspot, or he'll die. So he can't do it early, unless you mistimed.
What if he drifts back to the edge after charging for a long time? Not all characters can cover and punish a lagless landing when the opponent can land anywhere on one half of the stage, exacerbated by his ability to drift all the way back to the edge.
Oh, you absolutely can! You've been watching him charge up this whole time. You KNOW how far he's going to go, you just don't know if he's going to pull back at the apex. Don't commit. Just stand there. If he rockets far to get past you wavedash back with him and smash him. If he pulls back and goes for the ledge, fsmash him. Or dsmash him. Or something.
My best practice partner is my crewmate who mains Roy. He gets me like this all the time.
What about side-b, which often makes up-b not even a necessity?
Position yourself to hit him if he does it at you, forcing him to pull back. The attack and the grab have tiny little hitboxes that most characters can swat away. If you have no great offstage forward facing attack, then just be prepared to bait and punish it because it goes far. He can only use side-B once offstage, it's like a jump.