Even Final Cut Pro on iPad requires staying in the foreground during exports.
The iPad really does have great battery life on the other hand.
Scroll down to "Chip": https://www.apple.com/ipad-pro/specs/
There might even be some logic to that with each device optimized for it's specific best purpose. It also doesn't hurt that it makes them more money.
IMO they should do a hard turn and make iPadOS it's own thing. Give it the benefits of iOS but with macOS flexibility. Right now, it's essentially a bigger phone.
I'm pretty sure Final Cut Pro would export a video in the background of an 8GB MBA just fine.