Well, you'd need your other trait in Rich Parents or some other means of higher starting wealth (or starting above level 1) to actually be able to pay for your masterwork weapon. But yeah, if you can pay for it, you should be able to make it your HW, making it HAVE to be a non-masterwork weapon is dumb.
Masterwork transformation: It's great that exists! Prime, that's pretty lame if your Dm would have it wear off, instantaneous means the magic's gone, just the result remains. And you're paying the 300 gp, it's not like you're cheating the system.
That said...why does it always have to be magic that solves everything? Why can't a smith just enhance a normal weapon to become masterwork using the craft skill? Ditto for increasing the draw on a strength bow? Why is this crap impossible to alter without magical assistance?