I think it could work.

Basically, what you've got is a sort of usage-based improvement system, without some of the drawbacks. Like, the downside of usage-based systems is that it incentivizes repetitive behavior -- you do repetitive behavior to level up that behavior, and then once that behavior is leveled up there's an opportunity cost to doing anything else, so it keeps you further in repetitive behavior. This isn't in the player's interest or yours (you both want the player to experience a wide variety of fun things rather than experience a tiny repetitive sliver of the game).

By tying the upgrades to specific, named actions (of which there is a limited pool), you avoid the problem of someone swinging a sword at a friend 1000 times and then the friend healing themselves 1000 times, in order to level up in swords and healing. If there are only 3 opportunities to level up in healing magic per chapter, you just can't do that.

The downside of your "usage-quest system" is that it becomes a lot of work for your creative team. Can you push that much content in the amount of development time you have? Can you think up a different mini-quest for each possible level of healing? Are the agility quests more difficult or long or tiresome than strength quests in a way that it incentivizes strength builds in an unintended way?

Rather than hard-coding (or generating) specific quests, you could:

1. Identify places/times in the game you can only access by exercising specific skills (like a spot you can only get to by exercising agility, or by talking your way past someone in a clever way, or by winning a jousting tournament, etc.)
2. Put one-time skill-specific upgrade collectables in that spot (like Chrono Trigger's "tabs"). (After all, which felt better in Chrono Trigger, leveling up or finding a tab? Probably finding a tab. I still remember where some of them are.)

Then again, this almost entirely removes one of the perennial benefits of levels. Provided gaining a level is a real reward (e.g., that you get skills that expand your gameplay possibilities), there's an "anticipation" period before you level up where you keep playing in anticipation of leveling up. ("Can't abandon the game now, I'm more than halfway to the next level"), and then a "honeymoon" period after you level up where you keep playing because you have new stuff to play with and maybe there's a period where once-harder-things are now easy and you feel badass. That's a really effective cycle, and part of why RPG levels are now part of so many other genres.

(And why you have multiple systems that are "filling up bars", so that you spend more time in anticipation and honeymoon modes and less time in "neutral".)

That particular cycle is harder to maintain with a "collectathon" structure -- it's easy to be in the anticipation mode if you've spotted a "tab" and are figuring out how to get it, but when you don't know where any "tabs" are you're in neutral mode. Same thing with "usage quests". If you don't know you're on such a quest, or aren't on one and don't know where to find more, then you're in neutral.

Anyway, it's not a fatal problem. This is just to get you thinking about ways to keep people in anticipation mode without levels.

Because you're building your stats because on the quests you do. Rather than the number of enemies you've killed or number of times you've used a weapon, skill, or magic.

If you want to be a warrior, you'll do quests that will strengthen strength, attack, physical defense. If you want to be a thief, you'll do quests that will strengthen intelligence, agility, stealth.

In 'Fable' (one of the first two - I haven't played the others), you have four different experiences that act as currency:

- General experience can be spent on anything

- Three different attribute-specific experiences (I think they were Strength-based skills, Dexterity-based skills, and Magic-based skills).

When defeating an enemy, depending on what abilities you used to defeat it, you'd get that same kind of attribute-specific experience as well some general experience, providing a mix of freedom to develop your character how you want (using general experience), and also growth in the same area you are actively using (the other experience types).

Kill 10 slimes in a normal RPG would add EXP points and going to the next level will up all your stats. Move 10 rocks will increase your strength only. Kill 10 bears will increase only your strength and your stamina.

So to try to put it another way, the events (as I call them) only increase a particular stat (or two depending on the quest).

What if I take the "Kill a bear" quest, and I kill him by pushing rocks over a cliff edge onto his head? Your quest wouldn't recognize it, because it sounds like you are designing your quests to force the player to approach them a specific way.

Suppose I kill the bear via dousing it in gasoline and lighting it on fire? Or kill it with arrows from 100ft away? How is strength involved?

Suppose I kill the bear by running away from it, and luring it to try to cross a rope bridge, and then it falls to its death when I cut the rope?

Obviously not all these mechanics will be implemented in your game - my only point is underlining that your are forcing players into "one true way" of solving the quest, or at least rewarding them as if there is only one true way. i.e. your quests aren't a challenge of choices and thought, but a challenge purely of action, with the solution pre-prescribed.

When I "Kill a bear", regardless of how I accomplish it, the game pretends I really did "Kill a bear with a sword in close-combat while within 20 ft of its starting location."

Your design could certainly be made to work for a game or two, but as a general improvement over existing experience systems, I feel like there are too many cons and not enough pros.