I'm much more concerned that when I try to cast a mount, it takes 1 second or whatever instead of just being instant. Plus if I move a little too soon (after 1 second has passed and I've actually done the "whistle" to make the mount come out but before the mount actually appears) then I waste the cast and keep on walking. Great!

For example, in Tera, you can cast mounts instantly, and, well, it's amazing. Instant cast mounts. The best thing ever.