FTS - The Denisovans are usually grouped as a sub-group of Homo sapiens.
The diagram is absolutely not the last word on the taxonomy of our ancestors. So much is still to be worked out and new discoveries will change things in the future. One problem is that the popular press publish modest contributions to the science as if they were earth-shattering revelations that have changed everything. Progress is almost always slow and steady and open to constant revision.