A subject near and dear to my heart! My eyes aren't good so I have a very particular set of preferences, preferences which I have acquired over a very long career. I like to adjust the font size, <body> and <p> margins, and line spacing so I get exactly X lines of text on the screen, each and every time.
Before, I had to open the epub in calibre and do some editing. That got old. Finally, I've managed to do this with my custom build of Plato. Added a CSS tweak feature whereby I can long press on the main text and apply a canned CSS style to it. Boom! 20 lines of text on my Libra 2. No more fiddling around.
Shgmeless plug >>>
https://github.com/thataboy/plato/bl.../CSS_TWEAKS.md
This is just way too nerdy to ever see the day of light in any mainstream product. Heck, it's probably way too nerdy to make it to Plato proper. But yeah I think that's what it takes to achieve consistency, because I don't think you can expect publishers to standardize their formatting. They don't do it for print books (nor should they), There's an argument to be made for ebooks, but we who care are a very small minority.