Of course Killdal had the right to sell his own software. But good effort at splitting hairs, there. That doesn’t change the fact of where what became PC DOS came from. Sure, Gates and Allen became very wealthy off of that deal. Good for them. But don’t go trying to pass off Gates as being such a great technical innovator with DOS when someone else wrote it and what he sold to IBM was a rip off of CP/M.
MS made significant changes to DOS before they gave it to IBM. They worked day and night for months to get it ready. Even then, they gave Killdal the right to the result. Killdal simply did nothing with it.