I am fully for being able to level a skill as you use it, but there’d have to be some sort of limit to it so people dont just stand near a mob spawn point while having a macro running to use the skill every so often in a low level area.
As for skills with multiple attributes, perhaps they’d be more “hidden” and require you to use the skill in a specific way for the attribute to unlock. It would fit the whole exploration thing the game has going too.
For example, Highlander’s Cartar Stroke has the additional knockback attribute, but what if it wasn’t mentioned until you knocked back enemies with it X amount of times? So using it for bossing wouldn’t unlock it, as they can’t be knocked back. Instead, that would build towards unlocking the “No knockback” attribute.
I dislike paying for skill-related things in any game. I much prefer systems where skill upgrades are something you need materials or experience for.