What happened?

When flying with an armored elytra, the durability decreases very fast, even with unbreaking 3. After comparing it with unenchanted elytra and an unbreaking 3 elytra over a thirty-second flight, an unbreaking 3 armored elytra lose about 25 durability while the unenchanted vanilla elytra lose 30 and the unbreaking vanilla elytra lose 4. If we scale the armored elytra's durability loss to account for the fact that it has a bit more than 2 times more durability, we get 25 / 2.0833, or about 12.0002 durability lost.
Here are the elytra used in the test:

Mods used, to be thorough:

BetterEnd

4.0.10

BCLib

3.0.13

Fabric API

0.91.0

Fabric Loader

0.14.24

Minecraft

1.20.1

Relevant log output

No response

Other Mods

No response