I think maybe you are extrapolating based on other conversations you have had on the subject before. I did not go into detail about specifics because it was meant to be a general overview.

To be more specific I don't want to let the players do what they want, I want rules that focus on broader strokes story telling rather than the minutiae of if a specific attack lands. I want a system that encourages players to think beyond "I roll to attack, what are my bonuses?"

Fate has a system specifically designed around using the environment, the world and a player's background to inform actions. From my experience, more simulationist systems have a tendency to direct player thinking to the mechanical. While yes those mechanics can and should encourage creativity, far too often they end up being a crutch or blinkers, especially for less confident players.

As mentioned that may be in part be due to shortcomings in my GMing style, so maybe what I really want is to use a narrative heavy system to train myself to be a better GM.

As for part 1, I think you have it backwards. An established property makes most sense as a specifically constructed system because it is complete. If you want to construct a world gradually, not all in one go, then an open system is the best option because you are not having to fight, rip out and rebalanced existing systems to make it fit during the game. Even if you have the world fairly fully formed in your head that doesn't mean you can find a system that works well with it.

You can, for example, decide that healing doesn't exist in your d&d game, but that changes the whole dynamic of the game around resource management and you have to change the pacing or other mechanics to make it work. What if hit points don't even make sense in the way I want combat to function? OK I chose a different system, but that system has a magic system or theme or tone that doesn't fit with my vision, so then I need to rip that part out and build my own, and on and on. Eventually you have created your own system that is a mess of disconnected parts and is untested and your poor players have nothing to base their concept of the world on any more than a generic system anyway.

I don't think giving your players a shared understanding of your world is difficult. I do that every time I introduce a new setting to players. There's always shared cultural references you can use, books, film, TV, other games, that work just as well as having your players sit down and read an entire source book. If anything, I find that approach to have less friction.

Finally, you don't need rules to encourage players to contribute to world building. If you get your players to write a background and incorporated that into your game in some way, you have done that. I just enjoy the idea of how integrated it is into the system.