I too love my 12.9”, but yes device size a very personal decision. The best size depends entirely on how one wants to use their device, what one’s tolerances are, etc. I think if one wants to use their iPad with a keyboard often, or otherwise mostly resting on something, a stand or lap etc, and it’s carried around in a standard-sized bag/backpack anyway, then there isn’t much sacrifice in having a bigger device and one can really just benefit from the larger screen. On the other hand, if one often wants to hold their iPad, then a smaller one will usually be the better way to go. Or if someone is like me and just wants the bigger screen, to use with the Pencil for example, even holding it, then of course the 12.9” works best.
For me, I really like having the advantages of both a big and small iPad, so I have a Mini in addition to the 12.9”. As far as justifying buying two iPads, that is also very personal. For me, my 12.9” iPad and Pencil really help me with some work-related tasks that wouldn’t work as well on smaller iPads, so I have no issues justifying it. The Mini is much more of a leisure device, but I use it by far the most out of all my devices precisely because of its size, so it also earns its keep. One medium-sized iPad would be a bad compromise for me, worst of both worlds. But everyone is different.
