Except that other than combat (which gives each creature an XP amount)... any actions or quests or things that the PCs do or complete gains XP completely determined and at the whim of the DM. So even "non-milestone" XP is still pretty much "milestone XP" because the DM chooses how much XP to give for each thing. If the DM wants Level 1 to last six sessions, then the XP they'll assign to each quest in that time will be just small enough that it'll probably take six sessions to get there.No. Milestone XP doesn't make sense with that approach. Get XP for actually doing things and it does work.