Here’s how I would approach the decision:
1. What do I use theMac for when traveling?
2. What are the must have capabilities/
3. Can the iPad do all those things I will need to do when traveling?
If yes to 3:
4. Is an 11 inch screen big enough?
If yes, then use the 11.
If no, go with the Pro.
If no to 3, will the Pro do it?
None of this is really mission critical to me, so it's just about what would be the best experience. I am thinking 11" iPad for the airport and the plane, and the 14" MacBook for the hotel room, watching stuff in bed, typing. The 11" is just a tad too small to be the everything device for a whole trip, but it's fine for a plane.
Or potentially the 12.9" iPad Pro to just do it all - smart folio case for the airport and plane, magic keyboard for heavier duty use in the hotel room, watching stuff in bed, typing.
The more I use this 12.9" I just purchased, the more I think I might return it. It's beautiful, jaw dropping almost, but it's just a tad too big and unwieldy. I think the 4:3 aspect ratio also contributes to that. If they made a 12" iPad with the same aspect ratio as the 11", videos would appear the same size as they do on the current 12.9", without having to be so tall, and you'd save a bit of size and weight.
Or maybe I just stick with the 11" for everything and I use the extra weight and space to bring a Nintendo Switch and a book. The indecision lol...