That doesn't make any sense. Netherite armor already exists. As the carapace is comparable to Netherite in terms of getting the armor, it should be compared with Netherite in terms of using the armor. If PVP servers don't want items this powerful, they can remove netherite OR carapace armor. But Netherite is barely stronger than Diamond anyway, so if a PVP server really doesn't want stuff this strong, what they actually need to do is remove Diamond armor.
There is definitely a lot of work to do in trying to balance the extra enchant space with elytras not having it. I'm not sure what exactly is the difference it'll make, but that's what we should be talking about. Because carapace armor is as hard to get as netherite armor, it should be designed to be similar in power to netherite armor. That DOES make sense, because netherite armor DOES exist in the game.
Why? Is there no foreseeable way to add a weakness to balance out the effect? Why does elytra necessarily need to put a big hole in a player's defenses?