The advantages of the scientific method are easily lost if you don't have the whole package, which is why despite having aspects of the scientific method all over the place for millenia, things didn't really take off quickly until all the key pieces came together at the same time.

The point isn't to say that there's no prior art for any of Design Thinking. Of course there is. But unless all the pieces are put together in the same way, you can't claim prior art on the whole method.