There's no reason to impose suit ideas on other aesthetics. Instead of being motivated by your disinterest in suits, or belief that suits are dead and thus mostly costume-y, I encourage you find an area of aesthetics that you like. Perhaps that's 1930s workwear; perhaps it's 1980s counterculture; perhaps it's 1970s hiking style. Find outfits in that aesthetic that you like. Then consume a bunch of images and try to draw themes. Perhaps you'll find that a lot of 1960s workwear had rounded tops; perhaps you'll see that 1990s counterculture relied on a lot of colorblocking. Or whatever the themes may be.
You can then try to find ways to use these concepts in ways today to retain some of that spirit in a way that looks contemporary and not too historical reenactment.
If your belief is that suits are dead and no longer relevant, you don't have to study suits anymore than you have to study Latin. You can simply find literature you like — German, French, Japanese — and study those languages.
Workwear does not follow the same concepts as tailoring. The concept of "flattering" is not the same. You can't build up and extend a workwear jacket's shoulder because it does not have should padding and wading. This is obvious in real life but unfortunately not obs over social media because this format is useless for learning things. But if you could feel a suit jacket shoulder between your fingers and squeeze a button up shirt (your Ralph photo) or the Belstaff jacket, it would be immediately obvious.
But again, no reason to harp on about dead clothing. I don't talk about monocles and top hats to discuss how to dress today. So is the suit is indeed the new frock coat, you have been liberated from them and can now move on to whatever aesthetic excites you.