Xeviat
Dungeon Mistress, she/her
So, the AC is comparable to medium and then heavy armor. This allows strength or Dex builds with no particular issues.
the name, I get where you’re coming from but, there isn’t a better name, and Swordmage has history in D&D .
Yeah. Remember, heavy armor only hits AC 20/21 when a shield and the defense fighting style come into play. So Paladins and Fighters can get there. Barbarians, oddly, could get to AC 22 if they got a Dex 20 and Con 20 and used a shield, and even 24 with Con 24 and Dex 20. Which is ... weird.
The only other issue I'm seeing for Dex equals 10 + Prof + Int is that it will be tempting for a Wizard to pick up from multiclassing. Thus, you might want to hide the progression in the class itself, and just happen to give it out on the proficiency levels.