>>3794318the gameplay loop of an RPG is character progression. If there was a check threshold that required X amount hearts, and required the player to acquire heart pieces, then maybe it would be an RPG.
Some Zelda games have this. For example. Requiring a lv2-Shield to get past a certain screen. But arguably, a Lv2-Shield is just another tool. Navigating environments using tool is just Action-Adventure mechanics.
The real grey area is with the early Ys games. They look like Action-Adventure Mechanics, but require you to go back to town and buy the best equipment to even scratch the enemies in the harder areas.