The question was when it started.
on the armor side:
0e-2e: "medium" armor was strictly inferior to heavy armor. 0e and 1e rangers wore heavy armor though.
3e: Medium armor tops at 18 AC. Heavy at 19. But the best medium armor required 15 DEX to top AC and had a -4 ACP. So Braces/Gloxes/Gauntlet of DEX, light armor, and go full DEX.
4e There were no medium armors. Ranger capped at Hide.
5e: Medium armor was 1 AC behind Heavy naturally and didn't have a DR feat.
Rangers stopped being tanky in 2e. It was still a warrior and could do every other role. In fact it was better at dual roles than fighters.
But Rangers stopped being tank options in AD&D.
on the armor side:
0e-2e: "medium" armor was strictly inferior to heavy armor. 0e and 1e rangers wore heavy armor though.
3e: Medium armor tops at 18 AC. Heavy at 19. But the best medium armor required 15 DEX to top AC and had a -4 ACP. So Braces/Gloxes/Gauntlet of DEX, light armor, and go full DEX.
4e There were no medium armors. Ranger capped at Hide.
5e: Medium armor was 1 AC behind Heavy naturally and didn't have a DR feat.
Rangers stopped being tanky in 2e. It was still a warrior and could do every other role. In fact it was better at dual roles than fighters.
But Rangers stopped being tank options in AD&D.