Yeah! I can empathize with what your thinking. I went through the same process myself.. and have drawn many of the same conclusions. I'd love to get into details as to what I've decided but that is for another thread.
In-flight usage is only one element of a trip. On a cross-country flight it is the largest element, but still only one. (my extensive comparison of the iPad Pro vs. YB in another thread laid it out)
If one is traveling with an iPad Pro with the Smart Keyboard, it is very awkward to use in mobile scenarios like standing in line. The Smart Keyboard doesn't secure itself to the iPad and so the iPad must be held in such a way as to keep the ASK from unfolding. Removing the ASK in that scenario is not always practical and then leaves the screen unprotected.
Alternatively, if one is using a bulky protective case (and either no keyboard or BT keyboard), then it too can be a bit unwieldy.
This thread is asking for advice for the best iPad Pro for a plane so I'll try to get back to that.

My recommendation would be (and one I use and enjoy myself):
2018 128GB 9.7 iPad (non-Pro)
Apple Pencil (w/MoKo Pencil sling)
Smart Cover (use a clear skin for the back)
Apple BT Magic Keyboard
Shopping around, one could buy all of the above for the same price as the MSRP for the base 10.5 iPad Pro model alone.