Man, I just flew Economy from the US to India and it was even a struggle to use my 11" iPad Pro on that small ass tray table. No way I could manage a 14" MBP, I'd be losing my mind.
Now if you sit up in Business or First, completely different story.
Yes, this is similar to my experience with my older 13 MBP (which I believe is roughly similar to the 14 MBP size), in economy class, particularly on cheaper airlines. Vacation charters are the worst.
While the experience wasn't perfect with my 10.5" iPad Pro or 12" MacBook, it was nonetheless significantly better than with the 13" MBP.
I didn't frequently take business class. Very occasionally an outside company would pay for my flight so I'd be on business class, and that was noticeably better for space, at least on international flights. On domestic flights it depended up on the plane and airline. However, my workplace had a no-business class policy. I mean I could take business class, but I'd be paying the difference between business and economy out of my own pocket, so I'd stick with economy. And for domestic flights under 5 hours, I didn't really care anyway. The times when it made a huge difference was international flights but those business class flights were horrendously pricey, so I wouldn't pay out of pocket for the upgrade there either.
Note, there is also something called Economy Plus or Premium Economy or whatever. This was a grey zone for us and my workplace would cover it, so I'd often take that. This would provide more legroom. However, the seat and tray style may or may not be different. Sometimes the seats are bigger and wider with more room on the tray like in some business class seats, but sometimes not. YMMV.