In light of keeping everything simple, why not just say:
Light armor gives a +1 AC with a max of +4 Dex.
Medium armor gives a +4 AC with a max of +2 Dex. Disadvantage on Acrobatics.
Heavy armor gives a +8 AC with a max of +0 Dex. Disadvantage on Acrobatics and Stealth.
Add in shields, as usual.
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If you're trying to keep it simple, I don't see the point in differentiating between types of light and heavy and whatnot. Just give bonuses on the type, let the player and DM color in the specifics.
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Then special materials like mithral and such can make a difference to the base stats.
And magic, of course.
That's the opposite of what we (I) want, though. We want a
more complex armor system with tradeoffs, such that one character won't ~always wear a single armor, and where more expensive armor (within a given tier) isn't strictly better.
E.g., in 5e/BG3, a character will
always choose leather over padded, studded leather over leather, and a Dex-based character will almost never wear medium or heavy armor. In your suggestion, it'd remain the same except now there is
no non-magical armor progression or choice at all. A str-based paladin with 0 dex will wear [generic heavy armor], and that's that. The differences between armors are too extreme to swap between armors.
What I want, and what I think GM4Him wants, is a system where armor (within a tier) can be a meaningful choice. Does your rogue want the [light] armor that gives +1 AC and Disadvantage on just Stealth, or +2 AC but Disadvantage on Athletics and Acrobatics? An assassin might choose the latter, but a swashbuckler the former. Characters might even possibly swap armors dependent on the area you're exploring and enemies you expect to encounter that day/hour!
