The second axis is depth, which I'll identify as specific mechanics and subsytems designed to model/represent/handle/whatever certain specific actions. The low hanging fruit here is combat, which often gets far more mechanical attention than other things. To take Mythras for example, you have a bunch of special actions designed to make combat more granular and controllable for the player. Some might blanche at my assertion that granular equals player control, but I think it is a supportable position. If we take some thing like Free Kriegspiel as one end of the TTRPG spectrum, and with something in a crunch-drenched BRP game at the other end, I think this idea becomes pretty uncontroversial. The more skills, the more mechanics, the more specific buttons a payer can push to effect diegetic change the more specific control the player has. Why more specific control? Because that granularity takes some parts of the adjudication process out of the hands of the GM. A specific example might be the notional difference between adjudicating a roll vs a generic 'knowledge' skill in some sort of OSR game versus the cornucopia of academic skills present in a game like CoC. In the first instance the GM has rather a lot of latitude about what the PC might or might not know, but which becomes more fixed as the range of skills gets more and more specific. This isn't a value judgment, nor even something I'm completely sure of, but it makes enough sense for me to toss it out here and let people pull at the flaky bits.