All of which can be done without ability scores. They add nothing new.
I'm not saying they do. I'm saying they're a good starting base.
OK, that's exactly what I'm saying. Perhaps you're misunderstanding my position. What I'm advocating for is to by able to say "I'm a great Fighter" or "I'm a great Wizard" or even "I'm a hybrid of Fighter and Wizard", and then to, independently, also say "I'm great at breaking down doors" or "I'm great at persuading people" or "I'm great at reading books and finding information". Not to be all those things at the same time. Just to have greater flexibility in choosing what things you want your character to be good at.
There must of course be some tie-in to each other. But lets throw out skills for a moment, I'm fine with players choosing what skills they want to be good in. Everyone picks say, 3 skills and gets X value in them to start with and then gets Y points to invest as they choose in those or other skills. Sort of a hybrid 4e and 3.X system.
But I'm still not sure that class, on it's own, should contain everything. How do we resolve the greataxe-weilding fighter-wizard? How do we position him against the straight fighter-type and the straight-wizard type. Is he half as good as either because he's evenly split? That doesn't really resolve the issue of players being stuck with one specific score, now they need to stick with one class to be good at it. Does the fighter class and the wizard class get the same BAB? If they do, then a 5-5 fighter-wizard can hit just as well as the 10-0 fighter-only. He may only know half the spells of the wizard, but that still makes him basically 10-5 out of a possible 10. The fighter-wizard is better than both the fighter, and the wizard on their own!
I would make how much damage you do be based on what class you are,
So, BAB basically, applied to damage as well.
what weapon you are using,
we've got weapon damage types.
and what other build options you took. Not any ability score at all, so there's no "physical damage based on how charismatic they are".
But that's where it gets tricky. Take above. The fighter gets say, one "build option" per level, while the wizard gets one every other level.
So the wizard-fighter gets 7 choices. How many "build options" do we really need to be better with a greatsword? Two? Maybe three? All the while he's still gaining 5 spells(lets just say one per level for simplicity). The wizard-fighter can cast as a 5th-level, and hit as a 7th level. That still makes our fighter-wizard a 12/10. We're closer, but he's still sitting on more power individually than the straight fighter or the straight wizard.
And sure, it makes sense for strength to improve dealing physical damage. You as a player could certainly say that your fighter is good at dealing damage because he has a lot of muscle. But that doesn't mean damage has to actually be tied to the ability score called Strength. Just because you are strong doesn't mean you are good at using a weapon effectively to deal damage.
Effectively dealing damage and the amount of damage you do are often two different scores(which I'm fine with). Dex-to-hit, str-for-damage.
SAD is only dangerous when some classes are SAD, and some MAD. If noone is dependent on ability scores for combat abilities, then "SAD" and "MAD" are simply nonissues.
Sure, but we still retain the linear-fighter, quadratic-caster problem. Wizards get better at hitting, and also get better things to hit with, in addition to new option on how to hit. The fighter gets better at hitting, and new options, but never anything better to hit with, and if they do, they have to pay out the wazoo for it.
And if you localize mechanics to doing specific things, instead of having Ability scores that do all sorts of things all over the place, it becomes easier to balance the game. It's harder to "do everything" when each and every "thing" requires a different feat, or class feature, or whatever.
4e did that to an extent and you can see how well that was received(though don't get me wrong, I liked a lot of things about 4e).
I understand what you're getting at, but to balance things out we'd have to take a 4e "powers" approach to martial combat. Basically so every class would gain the options of:
Better to-hit/damage(through your BAB variant)
Better things to hit with(4e powers)
Build Options(the new feats, limited only by class or power choice)
X number of Skills to train in.
Sure, you don't need ability scores for that type of a setup, but I'm not really sure that says D&D to me. It sounds like a fine basis for a game and pretty easy to balance, but I'm just not really seeing "D&D" in that.