I think that the 12 Mini is also for previous Android users and potentially new iPhone users. There is no Mini with Android OS. There a very few quite ok small phones but nothing comes even close to the Mini if you are on Android and want something small. Many Android users are used to thin bezels for a long time so the SE could be a No-Go as a switch option to Apple. But the Mini could be. This is also important. No Mini alternative in the Android world. There are some 5.8 inch etc. but nothing this small with such a big display in comparison. Most are 6.1 and up. This is worth quite something for Apple if people switch because of the small size.
I really hope for a 13 Mini as some things are a little worth than on big phones. Battery is no concern. But I feel reception could be better. and some say it is on the bigger phones. Plus better reception Qualcomm chip with iPhone 13 saving more battery. Plus there is some work with the resolution, esp. display zoom, to be done. And the more models, the more Apple and developers will work on that.