Honestly, I seem to sway daily between thinking the 12.9" is too much and counting the days until I get rid of it and then liking it. There are some contexts were the 12.9" is amazing and then so many where it's sub-optimal. I've always felt like it's wasteful, but I think dual iPads is a pretty good setup if you can afford it.
Right now I have an iPad mini 6 and a 12.9" iPad Pro. I think my dream setup would be an 11"-12" iPad Pro with OLED fully decked out as my main personal computer and then a 14"+ iPad Studio/Pro for home use for special projects like drawing, external monitor with Mac, etc.
I think if I was forced to commit to a single iPad only I'd likely go for the 11" iPad Pro which gets close to the 12.9" with the scaled display of iOS 16.1 and can expand with external display support if needed.