I wonder if we can classify the different kinds of complexity and assess their relative popularity.
Player Facing Option Complexity seems to be both the most common and most popular form of complexity. lots of classes, feats, talents, powers, skills, spells, etc. Even games that are otherwise pretty light will sometimes layer these things on top (I put 5E in this category).
Then there is Fiddly Rules Complexity, where you have all the modifiers and subsystems, conditions and special circumstances. 3.x and now PF2E definitely have these. Even SWADE to some degree (although SWADE is definitely lighter than 3.x).
There is also Optional Rules and Dials Complexity -- games that let you define how the game works. Most toolkit games have this kind of complexity, some more overtly than others. 5E 2014 had some optional rules, while as I understand it Cortex is essentially entirely optional rules (like FUDGE).
What other kinds of complexity are there?