What is the practical difference between these ~exactly?
The difference is in practice.
So I have a system based on reflexes. Scientifically, warrior one has mastered defense for front attacks so his reaction time is only x milliseconds but he is bad on attacks from sides as his reaction is much longer. Warrior two has different reaction times and weaknesses.
So with a standard margin of error making reaction times longer or shorter and adding the random element, and I am also accounting all the player skill and tactics involved, out of 100 fights we get the statistics:
Warrior one has a %52 chance of hit.
Now if you make it the other way, that the statistics decide the combat results, then every fight becomes a case of chance.
So you are there standing, watching your friend one step away from being killed by the evil guy, you have your last arrow and it is the moment of truth. You will not miss. The statistics will say %90 chance. But it is not true, this is a shot that you will never miss. And you making the shot or not won't change the overall statistics anyway.
But if we let the statistics drive the results then it will be a moment ruined by dice. The two are very different, in practice. I am pro-dice but I also see the crudeness of it. For this level, it is too crude.
I'm for a defensive game engine that tracks reload behavior.

As to 'Skill > Chance', I agree completely, but I don't understand not equating weighted rolls with PC skill. The whole point of virtual die rolls is that improving their skill overcomes their circumstance. In Morrowind, did the PC not tend to hit more often as their ability to hit improved?
I wouldn't like that. I would like to eliminate the reasons behind the load, to make everything stay in the game. If players think it is fair, then they will stay. But I am OK for tracking in game repetitive actions and preventing that.
As I mentioned above, chance is ruining it. As it is about chance at core rather than skill. I like dice for the random element, not for a skill representation. It is about the margin of error which is not a hit or miss but +-3 degrees or +-20 milliseconds. If you positioned yourself in right position and attacked at the right time, you still score. This is player skill and chance but the skill mechanics produce these statistical results we were aiming for anyhow. This is about agency, the player will say he has the power and skill but he simply made a mistake. It wouldn't matter for him that our spreadsheet reads 2 out of 10 scores and if we give him better accuracy and better reaction times, he will score more. He is happy, we are happy.

Interestingly, sport games use player skill and character skill perfectly with this realization. They figured it out. We don't need that kind of player skill focus but it is possible to mimic that to a degree where players feel content about their influence. I personally hate hitting so many times with this always hit system. Damage sponges, there is no thrill to combat. Now with mods, as I block I feel powerful and as they block and the fight gets longer, it is more enjoyable. We both try to catch our breaths which is amusing. I wish I had a taunt button too.