Acrobatic in Armor: Yep

Just in case anyone wondered, armor is not particularly encumbering, certainly not enough to slow down someone by half. And while yes armor is really hot and somewhat encumbering and deserving of a penalty to endurance and to acrobatic maneuvers it has only a moderate effect on agility.

Most of 2e and before were written before we new anything about armor. So a lot of what shows up in books is flat wrong and comes from stuff like A Connecticut Yankee in King Arthur's Court more than any scholarship .

The limiting factor on armor was its cost, think "buying your own tank" cost not just a fraction of your starting wealth.

Now when I play B/X or Labyrinth Lord I use the rules pretty much as written. They aren't "historically accurate" but they work and thats good enough. I do tend to be generous though and I never penalize any Dex to AC bonus or anything like that.

A video for the interested, on You Tube showing a workout in what D&D calls Plate Mail or Field Plate depending on edition