From a PVE devastation perspective, hover being on the GCD is the clunkiest most annoying thing ever, this is already the slowest spec I have ever played and the only thing that keeps me awake is how methodical it can be played to be optimal but often in m+ you have to react, hover should be off the GCD and not interrupt current cast, just like shimmer.
-“Unaffected by the global cooldown and castable while casting” - i would spend 10 talents points to have this.
Hover is not on the gcd.
It has an animation lockout and a spell can be used leading into it like SS/AS or a burnout LF to get a little damage and potentially proc EB.
Movement is the skill expression of the spec, and with deep breath/slipstream resetting hover and how quickly you get deep breath back in m+ if you manage bombardments correctly, you can have basically (and usually literally) 100% uptime on hover every pull.
You can use both charges into the pull, get two more after your opening deep breath, and you have one charge and deep breath back well before they run out for two more charges.
Then you would be losing a ton of DPS simply because you don’t want to optimize your play.
I used to agree with you but then I started practicing entering hover during the GCD of an instant cast ability. Practice that intentionally for a day or 2 and it effectively allows you to play the way you hope to.
Instant cast living flame proc’d? Cast hover when you spend it. 
Shattering star into hover is goated when it lines up.
It’s not on the GCD it’s just got animation delay.
Use it after an instant or an empowered spell cast (because empowers start the GCD after you cast) and you lose zero uptime.
I can agree with hover not breaking casts