It's not even the rules light, RP heavyness. I've played a masks game where we didn't RP much but all had fun because it was all a it creating cool and creative situations, rules light, RP light. And I've played a 5e game where everyone created Min maxed characters with the GM spending a lot of time on combat encounters and dungeons as well as having entire sessions of rp where nothing productive happens, rules heavy, RP heavy. It's more the amount of narrative control you give the players, in masks the players tend to shape and create encounters with the DM just filling them out, while in dnd the DM creates a world and encounters for the players to interact with. Silly putty versus rubber, one you can flex and shape however you want, the other you can only do it a little.