To better fit the lore of the Elytrian, they should not be able to wear metal armor like gold, iron, chainmail, and Netherite as that would be too heavy. Instead, they should be able to wear diamond and leather armor, or one piece of heavy armor but nothing else (weight instead of protection). In addition, birds have dense bones instead of brittle bones, so the Elytrians should take 1/2 damage from crashes. To combat these strengths, Elytrians should have the Lean Muscles effect, which makes them take half a heart of damage while attacking in the air (recoil from the hit) and giving them weakness when on the ground.

This would rebalance the Elytrian, making it a much more versatile Origin.

Here's my personal opinion:

1. Though seemed reasonable, not a very good idea, it will cause more manual work for players to add tags in datapacks to compat with mod armors. In that case, if the player already have the knowledge to make datapacks, they can make a datapack following the doc and override the power themselves. So it's not a work that should be done on the official side.
2. It does makes sense actually, it is truly weird for elytrian to take more damage from crashes.
3. The idea of recoil is good, but the weakness part seems duplicated with the current restriction.

Actually, Origins is highly customizable, all of your suggestion can be realized in a simple addon datapack, which is the best part of the mod. You may just read the docs or join the discord server for help on addon making. It's actually not mandatory to ask the author for changes which overrides other's opinions and breaks consistency between versions :)

I think that they should make it so any armor value over "x" causes them to be too heavy to take off. So they can still wear the armor, just lose the ability to fly.
And make it so if you jump off a cliff and deploy wings, you just fall harder and take damage. ??

I'll make a datapack to test it out.