I don't recall saying anything about a directly underneath shot. I've never attempted one nor would I. I heartily agree with you on that point.
I certainly wouldn't compare myself with Byron or Howard. I would wager either of those men could out shoot either of us with a bow of ANY length.
Since you mentioned it, Hill did shoot long bows. Then again, he didn't have access to modern, short R/D bows. If he had, it is possible he would have chosen one of them. That is something we will never know. He also used wooden arrows. Had he had access to carbon arrows, do you think he would have used them?
Howard was Byron's hero, according to Byron, which is why Byron chose the longbow in the first place. His trick shots are taken from 10 to 15 yards. He says so in his book, and I have seen him in person. With his vision and hand-eye coordination, I don't think it would matter much what he shot.
On the other hand, I don't think I could shoot an aspirin out of the air with a bow of any length if my life depended on it. I can and have shot whitetails at ranges of 15 to 22 yards with 58" to 62" longbows. None of them seemed to notice the difference.