I’ve been a huge fan of the mini + 12.9 combo since the first 12.9. I’ve actually never been a fan of the middle size even when it used to be the ONLY size.
Nice to see more people seem to joining the combo club! Welcome! So it was really just the old design holding you back all this time, eh?
Planning to do the same combo here! 2017 iPP 10.5 currently that is getting long in the tooth. Work is mostly windows based (X1 Yoga), personal laptop as a 13" M1 MBA (can access work machines remotely), and personal desktop a mid-2017 iMac.
I've soured on the 10.5"/11" size over the years: Not great to use with Sidecar as a second monitor when traveling, not super portable, very cramped if I do anything split screen. So it's mostly relegated to take notes occasionally with the Pencil and watching videos while flying (not a lot of that the last year).
Hoping the iPP 12.9" will be: better for note taking, PDF reading and annotating (for conferences/journals, I'm in academics), better split screen, better sidecar (effectively dual 13" monitors with the laptop), and some easier (family) photo processing (bunch of old scans I need to go through in Lightroom). Planning to use with both the Magic Keyboard or Smart Folio, depending on if I have a laptop with me.
The iPad Mini I plan to then be the main around-the-house personal device, or the tablet to bring when traveling if I don't want the weight/size penalty of the iPP 12.9" (depending on how much I need the dual monitor support)-- whereas the iPP 12.9" will be very much focused on being a complementary device to either laptop.
Granted, it feels a little silly that if one iPad is useless, two will be useful.