All previous generation Titan models have been cut down chips as well TU102, GV102, etc.

With one exception: the Titan V card that I mentioned which comes with the GV100 chip. But as I mentioned, that one targets a very different market segment with HBM memory, which the "RTX 3090" obviously doesn't target, since otherwise it would come with HBM2 memory like all the GA100 products.