Pfft, for someone who must have played the game a lot, I'm not surprised you said that! About adjusting position midair... yep, that's asking a bit much, because no game has physics like this any more.
Super Mario All-Stars was one of the first SNES games I got when I was a kid, so I played it a lot back then. I remember getting it on Christmas day and playing it nonstop for more than 7 hours until I got a headache, I think my parents had gone out, since I wasn't allowed to play for more than 2 hours per day at that point in time.
It feels like running for 1 ms longer is the difference between jumping across a wide pit and falling halfway across. When it's that crazy, I think adjusting midair (slower than later established, at that) is a bit less of a concern
For speedrunners I imagine that running for a few less frames does make a huge impact, but for casual playthroughs I think the game is pretty lenient, and the issue becomes less about clearing the pit and more about jumping too far and the momentum causing you to slip off a ledge, which is where repositioning comes in handy.
The Lost Levels is much more unforgiving, I remember a jump where your running speed actually matters, you need to reach full speed and jump off the very edge to reach the other side. If you get too close to the edge, the screen will have advanced too much and you won't have enough space to run, so you're forced to kill yourself and try again, unless you're playing as Luigi, which makes this jump a bit easier, but the rest of the game becomes trickier because of his slippery movement.
I don't think the game is bad, but oh my word, it's definitely a game of its time. I do feel like it holds up well enough, ignoring the tedium of getting to levels after game over, though. And of course, it should be obvious why game over ends up being so frequent.
I just found out that in the original NES version, when you get a game over and get sent back to the title screen, you can hold the A button before pressing start, and this will also send you to level 1-1 on the world you were in, which is pretty cool, but apparently it's not mentioned anywhere in the manual.
