Characters and Letters aren't the same thing lol, a letter is a character, but a character is not necessarily a letter. Characters can be spaces, numbers, or anything else really.
When it comes to 3-character/3-letter names, it depends on the letter/character.
Something like 45t, R8n, Trq wouldn't be classified as rare. Names like God, Big, Sin, or Zap are all rare.
OT: They're all decent names, Fort is the best one out of all of them