I always found KOReader to be too fiddly for ePubs, has that changed recently or have I been doing it wrong? I want a set of sane defaults to be applied to every book, I don’t want to tweak every book individually. This leads to distraction for me
You can set defaults for all books. Simply long press on the option you want to be a global default. That said, it can still be fiddly since different books respond in different ways. Most of that seems to be due to differences in how publishers handle formatting, but I'm fairly certain that some of it is due to how the renderer handles things.
It’s still the case in my opinion. Yes, you can fiddle to make it work. You can set sane defaults. The heuristics for applying styles etc apparently are not clever enough because sometimes you still get strange results. Comparing it to the default Kobo reader is like using a Mac vs a Linux DE. As I’ve gotten older I find I no longer enjoy tweaking every possible parameter :)