I also love my Mini but I tried a 12 again, as it was on sale, and I can read so much better. Not within iOS itself but within third party apps. Text size in apps is soooooo small on the Mini and I am not the youngest with the best eyesight. Reading stuff within a third party app is way way nicer on the normal 12. Within iOS you can set the text size to your liking, not so with almost all third party apps I use. And of course video is nicer too on a big screen. Battery isn't, at least on the first day, that much better but it was the first and second day of owning the normal 12, it needs some time.
But after using the 12 for two days and the Mini before I just can't go back to a "normal" big sized iPhone. Within the iOS system everything just seems bigger with some more content showing, nothing special there. As known iOS doesn't take any advantage of a bigger screen. Just look at iOS on the Pro Max. It feels like iOS is still developed for smaller screens (iPhone 6, 5, 4S etc.) and they never really adjusted iOS to all those sizes for taking advantage of the bigger screens.
At the end after all the months and owning a 12 twice for a short time I think I am gonna stick with my Mini, even with the display of my current Mini being not as sharp and cool as that of my current 12. Mini display is more yellow and a bit washed out compared to my new 12. But the Mini is just the perfect size for my hands. Not too small, not too big. Not too heavy, not too light. Perfect! Now if Apple could only get the display mode settings on the Mini right. In my opinion standard is too small where zoomed mode is way too big.