The argument"MCH/Bard have utility so their damage should be lower"

[Durendel]

First off the change to WM was a recent change so do not try to act like this was around the whole time. Second this means that they more or less actually made it a choice you either have it on or you don't. Chances are that you will just have it on for your opener and if you feel safe for 15 seconds you will use it and or the most likely scenario you will just turn it on to line up with your barrage imperial arrow combo. Just because i do not play the job does not mean that I do not keep up with whats going on with the job.

[Durendel]

which in turn means you still get to keep your mobility accept for the occational 15 seconds which will be used for specific abilities as stated before

[Aiselia]

the change to WM was a recent change

And before the change, your suggestion would have made less sense since it had a 3 sec cast time, and stopping DPS for 3 sec to turn it on and shoot a couple shots then turn it off again would be even worse.

your opener

So why make it a song? Why not just a 15 sec buff with a cd that syncs with our other cds?

If we're only supposed to use it sparingly as a damage bonus every couple minutes, then it was designed poorly and should have been just another cd.
If we're supposed to actually use it as much as possible, then it was designed poorly because Bards were not designed with cast times in mind, even ignoring mobility.

Either way, it was designed poorly.

Or to be more accurate, it was designed well for the Machinist, when they made it. It was then transferred to the Bard as an afterthought poorly.

i do not play the job

Then you don't know how the class works.