I'm taking 5e as-is. If you have a houseruled variant down that deep, naturally it will be different.They are on DEX now, hasn't always been that way as I pointed out. Finesse weapons are the greatest offender to making DEX too strong IMO. We play finesse can apply to attack rolls, but not damage, STR still mods damage, even for missile attacks.
Technically it is a common magic item. And amusingly cheaper than normal plate (!).So, your answer is magic plate? Mithral is only under magic items... so not very common IMO.
Even without that, the cost of low str in heavy armor? 10' of movement, that's it.
That isn't great, but it is a level 1 spell whenever you really have to move.
Sure, you don't want that archtype in your world.I know what you are trying to do, I just don't agree with it. A priest who relies on faith to protect him and doesn't work to protect himself (i.e. DEX) is going to get hit and die.
No, "Swordmage" is a 4e class that was a fully featured front-line combatant who protected allies. "Bladesinger" is a wizard first with very limited front-line combat capabilities.The "swordmage" is basically the bladesinger, just for non-elves.
It needs to be as hard to hurt as a paladin in full plate to fullfill its role. Making a swordmage class that was a half-caster would be practical (and its own exclusive spells, like paladins/rangers have).