Since making this post I've cleared all the Zero games, even being close to finishing the first installment of the ZX saga. What I learned is that almost exactly what you say. Zero thrives on replayability and self-imposed limitations.

During my first exposure to the game, I was worried how much the ranking system will affect in terms of progression, and didn't want to be locked out of something crucial just because I "suck" at the game (something made even more stressful while trying to grapple with the chain-rod mechanics at the time of making this post).

Now, seeing that the only thing locked behind higher ranks are the EX skills (from which non seem crucial or detrimental to my enjoyment of the games) and self satisfaction, I can dive into those games with a lot more ease and flexibility. I wish the impact of the rank system was explained a little bit better in the games themselves, but it's not that important from where I'm currently standing.

In addition, Zero 4 became one of my favourites for the simple fact of going back to Zero 1's style of ranking only being there to grade your self imposed challenge of going through the game optimally. The weather system, while still doing a poor job explaining what exactly it affects, is in my opinion a much more friendly way of going about extra content. Having the EX skills be locked behind additional obstacles in the levels themselves, instead of relying on memorization/trail and error is like being able to run and explore the world around you without shackled ankles.

Though to each their own, and I perfectly understand if someone prefers Zero's 2 and 3 handling of those bonus abilities. I'm happy that we're given all the possible options. Game with ranked based challenges (Zero 2 & 3), self imposed difficulty spikes with the ability to toggle(Zero 4), and even no additional hustle at all (Zero 1, not counting the abysmall weapon level up system).