As stated, it doesn't provide sufficient functionality, and can functionally be bypassed as well.

Current behavior:
If a player with the flightless effect, which disables their wings, equips an elytra on any slot, back or chestplate, they're able to utilize the controllable forward momentum wings give, and can bypass the flightless effect.

Expected behavior:
Flightless disables the wings functionality altogether preventing users from starting the elytra flight state without an elytra.
This would improve potential compatibility with other movement mods that utilize jumping during air-time, such as parcool, or double jump mods.