I don't understand Mastery

So STR doesn't raise minimum damage at all? Is that why DEXless players are so concerned with mastery? I have heard several instances of people speaking of how important it is to them, but never really understood.

It does raise minimum damage, just less so than DEX.

It's like this. If mastery is 60%, a certain amount of STR will add 60 minimum damage and 100 maximum damage. If mastery is 10%, the same amount of STR will add only 10 minimum damage and 100 maximum damage.
That amount of DEX will always add something like 25 minimum damage and 25 maximum damage.

And remember that these are only for swords. As soon as you equip a bow or gun, STR and DEX reverse roles.

What affects this magical... magic term? Luck? INT? Magic attack? A combination of these?

Magic attack times itself.

Edit: Going to sleep. G'night and have nightmares about numbers Sarah