#i don't even have anything in particular against milestone leveling

[imsobadatnicknames2]

That is, in fact, still assuming that players will inevitably have the same linear set of predetermined encounters, just that they will overcome them in different ways (and with choosing how to overcome the inevitable encounters the GM puts in their path being the entire extent of their agency as players).

Most old-school adventures (particularly those based around megadungeons such as Barrowmaze or Stonehell) have dungeon exploration that's a lot more open-ended because most dungeons aren't meant to be fully explored in one go (or even fully explored by a single party at all), so the GM a has a lot less control over what encounters players do end up having and in what order. It's not uncommon for these type of adventures to conclude without the players having visited entire sections of the dungeon.

You could still argue that by designing the encounters the GM is setting the MAXIMUM amount of XP that players could *potentially* end up getting, but the amount of that XP they end up *actually* getting during play depends a lot more on the players than on the GM, so it's not equivalent to milestone leveling where it's, in some way or another, entirely up to GM fiat.

If there’s one mechanic the addition of which would significantly improve any edition of D&D that does not already have it, it would be the dungeon turn. Just that little bit of structure and procedure would communicate so much about how the game is played.

And if there’s one mechanic the removal of which would improve any edition that does have it, it would be milestone leveling. Get that arbitrary nonsense out of here!