But someone with an 18 AGL doesn't represent someone who has been trained in the use of armor since birth. It just represents someone who's more naturally Agile than most everyone else.
With the rules as written, I could have a Wizard with 18 AGL in Plate Mail. His AC would be 21. I could have a Fighter whose AGL is 8. He would have a 17 in AC.
How does that reflect training?
And people in Plate Mail were exceptionally less Agile than, well, anyone without it. Plate Mail's advantage was that it was hard to slash or puncture with most weapons. Most people who fought in plate mail did so on horseback fully because it was nearly impossible to charge in or to move at much more than a steady walk.
You're free to disagree with me. But as it stands, Armor seems odd to me at this point.
You know I would never disagree with your. *grin*
But... in DCC RPG (and other d20 OGL type games), the training, etc... come in additional HPs that the warrior has.
The armor is a static number. Steel is Steel.
AGL provides an innate ability to dodge attacks. Not related to Skill.
Skill is part of what makes up HP's.
Look at it this way. A 1st level Warrior with 8 hps and a Wizard with 3.
The both get hit by a Long Sword for five damage. The Wizard keels over. The Warrior's training allows him to take a far less serious wound.
Side Note: In 3e DnD, higher armor types have a maximum DEX (AGL) bonus allowed to simulate the turtle effect. That would be easy to add to DCC RPG, but I do not think it would be totally necessary as ability score bonuses are going to be far less than in earlier editions. Anyone with an 18 AGL is probably going to be a thief and not wearing plate.
(As a side point, I do like the idea that some other game systems have where STR does bonus damage, and AGL provides bonus to hit)