Clip Studio Paint has tone layers, which can be made as such, and there's a function to shift a layer into a tone one, so sometimes I'd just draw it as a tone, while others I'd make a gradient of grays and then turn it into a tone layer, to only fine tune its look afterwards. It's a bit of work and can be awkward to fine tune density and frequency to give it the shade you want, but I really like how the art comes out, so very worth the effort.
Your gripes with the gameplay are understandable, I was aware it was a really weird concept that would be hard to follow even if I eased it in little by little, so I went with a bucket instead of a dripfeed, and hoped for the best. Unprofessional, but I'm fine with not being for everyone.
The development of the ideas comes out through talking with Edrillmond and Sidrillta on the friend events, but it doesn't come to its conclusion in the mainline story because I chose to not put the True End in and risk not finishing art assets. My writing style is intentionally puzzling and asking you to put a lot together by yourself, but with so much to read and so few clues, I can't blame anyone for not seeing the thread. You could say it's one of those "just read 300 chapters to understand it" books, and unapologetic about it.
And about the shoehorning, I'd say it was half-half, in parts the story was shoehorned into the theme/game, and in parts the the theme/game was shoehorned into the story. However, I wouldn't make this game, with this setting, with these mechanics, without the theme of spinning behind it. It does sound forced, but it was borne from the theme, so it is ambivalent (to me). A confusing game and concept, but if you didn't tell me to write about spinning, I really had none of this in mind. Before the theme reveal, my idea was about fighting zodiac themed bosses in a sengoku-like school setting, and when spin came out I almost gave up because I couldn't make it fit. Faced with giving up or forcing my way, I chose to force my way.
I'm happy you could see through my throne of lies partially, but I'm sad I couldn't make you interested enough to pursue the full picture of the story and understand the many confusing elements of it.
Thank you for the great feedback, I don't think anybody else could offer words that would make me get so lenghty about the pre-development stage and my thoughts and feelings on what I composed and wrote here.