@Tactician
I'm aware of spacey pressure frame data and what you're saying about early/late aerials during pressure iterations is essentially correct. It just doesn't take into account that there are exactly 0 top spacey players that go about pressuring a shield with aerial->shine->aerial->shine->repeat. And even if there were, the holes in this kind of pressure can be beaten by grab by the same theory that up-B will beat it.
The thing about the holes however is that human reaction time isn't quite so fast to be able to react to which particular timing a spacey uses each time he decides to hit your shield. The only one I can actually react to is if Falco (or Fox) does a very early aerial on your shield after shine.. probably because of the visual cue it gives for me. Late aerials however are incredibly hard to react to for the same reasons that tomahawk grabs are hard to react to; nothing happens until it's to late in a sense.
You said "at worst this beats late aerial shield pressure mix ups." Grabbing right after shine does too lol.
In any case, I'm not trying to discourage you from exploring up-B OoS by any means. It just seems that so far up-B OoS only beats shield grab as an option in three situations which most of us already knew. 1) The opponent is in kill percents (which I mentioned before), 2) It beats shine-grab, and 3) Human error in grabbing by a margin of 2 frames (in all scenarios where you can up-B OoS successfully you can also shield grab successfully except for shine-grab).
This of course is not considering the differences in risk involved between whiffing either up-B or grab.
As for spacey pressure in general, make sure you keep in mind that there are many more mix ups to spacey pressure other than early/late aerial. I'd hate to see a Falco come in on your shield with a dair->shine->early nair, but with the nair faded away and then you react to the early nair with up-B OoS and then get punished really hard for it :/.