That's what I'd do if I'd make a Heartbreaker.
But it would be interesting if Spell DC were based on 2 or 3 scores.
Like instead of
Spell save DC = 8 + your spellcasting ability modifier + your Proficiency Bonus
it's
Spell save DC = 5 + your 1st spellcasting ability modifier + your 2nd spellcasting ability modifier + your Proficiency Bonus
So Ranger would be 5 + Wisdom modifier + Dexterity modifier + Proficiency Bonus
Wizard: 5 + Intelligence modifier + Wisdom modifier + Proficiency Bonus
Sorcerer: 5 + Charisma modifier + Intelligence modifier + Proficiency Bonus
Warlock: 5 + Charisma modifier + Constitution modifier + Proficiency Bonus
Cleric: 5 + Wisdom modifier + Charisma modifier + Proficiency Bonus
Druid: 5 + Wisdom modifier + ???? modifier + Proficiency Bonus
Paladin: 5 + Wisdom modifier + Strength modifier + Proficiency Bonus
don't need to change base DC if you make everything, including DCs as two ability based.
Fortitude save: str+con
reflex save: int+dex
will save: wis+cha
but I would tie most spell DCs to mental stats or Con
Sorcerer: cha+con
Druid: wis+int
Paladin: wis+cha
warlord: int+cha
ranger: int+wis
rogue: int+cha
Leave primary attack stats out of spell DCs
AC: 10+dex+int+armor, int can be a variable depending on the class(Con for barbarians, wis for monks, cha for some subclasses)
melee attacks: str+dex
melee damage: 1H str×2, 1H finesse str+dex, 2H damage str×3, 2Handed finesse str×2+dex,
ranged attacks: dex+wis
bow damage: str+dex
crossbow damage: dex(higher base damage, slow reload)
now as you have 2 attack stats, some features can replace one of those with one that fits your class/subclass
I.E:
true strike for wizard can replace either STR or DEX with INT or WIS
replace lower of STR or DEX with higher of INT or WIS, but not both.
but as for number of ability usages, I would avoid having abilities anything to do with it.
either a fixed amount at certain levels or prof bonus based.
