Sure it was possible to make your own drumkit on the Tyros3 but only with help of the computer and the voice-edit program.
But now it can be done at the Tyros4 itself and that is a real step forward.
And , which is important, it can be done easely.
Importing Waves is another chapter, more complex.
That is why I prefer the way of drummapping which is now possible on the Tyros4.