Scratch Space

At character creation, you should have almost all of the core skills you need, although there is room to improve if you want to.

You should have minimal power, but will gain plenty of it as you level.

Destiny is something that occasionally empowers you to do awesome things (ults), and becomes more commonplace as you enter epic level (never really routine, though).

Toolkits, Skills, and Powers

The idea of the Skill pillar is "everything you need in your basic toolkit", i.e. what an Overwatch character has, or maybe a 20-30th level WoW classic character (YMMV). Power, therefore, contains everything else.

But this implies that magic-users will need some spells in their Skill pillar, and fighters will need maneuvers, and enhanced will need superpowers, etc...

So while the option remains to (confusingly) grant some powers in the Skill pillar and others in Power, maybe there's a way to keep things cleaner.

What if we imagine all extraordinary/supernatural/spell-like abilities as belonging to one of three power levels (skill, power, destiny), with each working differently?

Skill Tier powers are typically at-will, no cost, highly versatile, and minimally powerful. Examples:
- Create Phylactery
- Channel Divinity (turn undead, power word: shield, etc)
- Immolate
- Wild Shape
- Contagion
- S6 style rituals
Power Tier abilities should have a cost, but otherwise not too risky to use. Examples: most spells above rank 1
Destiny Tier abilities are Big Magic. They have a cost, and impose risk. They may only be available in certain situations.

One possible (fairly simple) model would be 3e Cleric Domains. They had a basic power (skill tier), and a progression of power-tier spells. Just throw in a Destiny-tier use, and you're good to go!

If you spend a Skill Point (or whatever) to gain--let's say--the Faery Invocation skill:

You immediately gain the ability to Summon Sprites, the ability to communicate with Faeries, Faerie Fire, etc etc
You may spend (insert currency here) to acquire more powerful abilities, such as Magic Fingers, Jubilation, and Wonderland
You may spend (insert alternate currency here) to acquire bindings such as Fey Step, Mystic Eyes, and Glamour
When suitably inspired, you may attempt to Call Upon the Host

Similarly, on the fighter side, you could acquire the Stealth skill:

At will, you can hide from enemies to gain advantage or inflict critical damage
You can invest in more powerful abilities like Vanish, Sap, or Snipe
Epicness? hmm....maybe not

In a way, these are almost classes, but instead of something broad like Warlock, they are more like power disciplines or mundane skill groups (melee, ranged, stealth, etc)

Musings

It seems abilities come in three primary flavors: Attributes, Skills, and Powers.

The problem is, we don't really need all 3 at once.

Power gameplay is pretty satisfying; your choice of powers known, and your choice of what power to use in any given situation, are the core gameplay loop. Numbers are irrelevant--glass cannons assume the game is balanced around them, whatever the hell their numbers are, and any effort to make numbers more interesting (e.g. all 3 stats playing into spellcasting) is unnecessary if casters are already having sufficient fun. For these characters, only power selection matters; attributes and skills are not relevant, nor are details about numbers.

Enhanced gameplay is a bit different; the idea is to sacrifice some versatility and power depth (relative to the Glass Cannon) for a numeric edge against non-Enhanced. Numbers do matter somewhat--if only to provide a basis for a relative difference--but power selection is still king; it's just that said power selection includes bindings, superpowers, and higher stats.

Fighter gameplay is, as far as we can tell, not a thing. Pure fighters are nothing more than a debased version of Casters with less breadth and a hard cap on power depth well below Epic. Hybrids, on the other hand, behave largely like Casters--it's all about power selection. The numbers need only be reasonably balanced.

Final score:

Attributes: F (nobody cares about them)
Skills: D- (nobody cares, except maybe non-casters during the few utility challenges not trivialized by a Caster)
Numeric Details: C- (Enhanced care a little)
Power Selection in Character Creation: A
Power Selection in Combat: S

This is a pretty sobering discovery, considering how much of system design has gone into attributes, skills, and numeric details.

What system does this suggest? Well, let's whip one together, real sloppy:

2 powers per level
Ignore Mana for now (or assume 2 per level, or w/e)
Powers can be swapped for:
- Upgrades
- Bindings (currency tbd)
- Superpowers (same as bindings?)
- Ability scores

That's basically it. Ability scores probably exist, and skill checks do to, in some fashion, but...who cares, other than a third of PCs who just want to ensure they have a small edge?

Notes: actions and reactions should dominate; passives should be quite rare. Example: intervene > 5e protection warrior, parry > AC boost, lunge > extended reach.