It's an interesting question, but I think to get a true answer (or at least one that more closely approaches your thought of 99%) we need to really consider things under two different parameters--
1) In a perfect world, would we be happier with the fixed quirk, and
2) If the quirk (and only that quirk) was fixed, would it be important enough to us to actually buy a new copy of the book?
So something like you mentioned about the Index... sure, in a perfect world if the Index in the Player's Handbook was better and more intuitive, I'd be fine with having it. And I don't know if there would be anyone who would disagree.
But... if you were to ask me if I'd buy the book over again to get a "fixed" index.... I'd say, no, I don't have enough of a problem with it that I'd bother spending the money.
And this is where you'll probably have a hard time getting into the high 90s. Because while of course there are things you could "fix" that would make the game perhaps slightly tighter, there are none that I can think of that would warrant buying the book over again just to get. Because quite frankly... all the niggling little things that you could "fix" (like the spear/trident situation)... they are all so easy to amend if we need to on our own that they don't warrant re-doing the book.
If people find the current Stealth rules not to their liking, they probably have already ruled on it.
If people find the disparity between Barkskin's fluff and game mechanics bothersome, they probably have already ruled on it.
If people think the sorcerer needs more sorcery points, they probably have already given more out.
If people think more monsters need to be vulnerable or susceptible to the individual categories of slashing, piercing, or bludgeoning non-magical weapons, they probably have already given those out.
If people think dragonborn shouldn't be a main race in the game, they probably have already restricted them.
And so on and so forth.
We might be able to find 90%+ consensus on any number of things that in a perfect world we'd be happier if they had been different. But nowhere near that much if it would warrant purchasing a new copy of the rulebook to get.
1) In a perfect world, would we be happier with the fixed quirk, and
2) If the quirk (and only that quirk) was fixed, would it be important enough to us to actually buy a new copy of the book?
So something like you mentioned about the Index... sure, in a perfect world if the Index in the Player's Handbook was better and more intuitive, I'd be fine with having it. And I don't know if there would be anyone who would disagree.
But... if you were to ask me if I'd buy the book over again to get a "fixed" index.... I'd say, no, I don't have enough of a problem with it that I'd bother spending the money.
And this is where you'll probably have a hard time getting into the high 90s. Because while of course there are things you could "fix" that would make the game perhaps slightly tighter, there are none that I can think of that would warrant buying the book over again just to get. Because quite frankly... all the niggling little things that you could "fix" (like the spear/trident situation)... they are all so easy to amend if we need to on our own that they don't warrant re-doing the book.
If people find the current Stealth rules not to their liking, they probably have already ruled on it.
If people find the disparity between Barkskin's fluff and game mechanics bothersome, they probably have already ruled on it.
If people think the sorcerer needs more sorcery points, they probably have already given more out.
If people think more monsters need to be vulnerable or susceptible to the individual categories of slashing, piercing, or bludgeoning non-magical weapons, they probably have already given those out.
If people think dragonborn shouldn't be a main race in the game, they probably have already restricted them.
And so on and so forth.
We might be able to find 90%+ consensus on any number of things that in a perfect world we'd be happier if they had been different. But nowhere near that much if it would warrant purchasing a new copy of the rulebook to get.