One of the main issues here is that without the hard work and financial input from Yamaha, there would not be a brass* sample on which to base your new super-modified version.What is this? Why is it so hard for you to distinguish between copying a sample one-to-one and make a whole new patch of it by virtue of synths engine?
It's that original hard work that copyright is supposed to protect and reward.
It may seem absurd that it's illegal to mangle a simple sound beyond recognition and call it your own, but if brass samples are really easy to create, why not make your own in the first place?
"No time for that" you say, and here is the problem ... someone else did have the time, and they don't want other people profiting from it without their permission.
Peace,
Andy.
* brass sample used as a simple example here ...
