I was thinking about Legend Points, but they seem pretty similar to the Inspiration mechanic in D&D, and I absolutely sucked at remembering to dish out Inspiration in my campaigns. Just sticking to XP - which is core to progressing and unlocking new features - seems simpler and easier to remember, personally.
As for the second point… just look at the examples in the OL rules on milestone progression:
Level 2: The heroes thwart one of the three foes threatening Woodshold.
Level 3: The heroes discover the Cult of the Dragon.
Level 4: The heroes prevent the cult’s Ritual of Three from being completed.
Level 5: The heroes retrieve the treasure at the bottom of the Sunken Star.
Level 6: The heroes end the conflict between the barbarians and the Collectors.
Level 7: The heroes free the village of Hilltop from the grasp of the vampire Tessa.
Level 8: The heroes discover the secret of the Ruins of Mastika.
Level 9: The heroes find a way to weaken Dezzer Kai’s power over the land.
Level 10: The heroes defeat Dezzer Kai.
Those all sound like pretty important story beats, and if the players continually subvert from those plot points, then they’re not really playing your campaign as planned.
If they don’t thwart one of the three foes threatening Woodshold, do they not get to level up? Does Woodshold get burnt to the ground and the campaign ends?
Anyway - I’m getting off-topic here LOL. Maybe OL isn’t the right system for me and I should keep researching for my holy grail D&D alternative. 