I believe there are many reasons to think this is another species. The simple number of things that “don't make sense” if we view homo floresiensis through a human perspective is the first warning flag, even though it isn't a scientifically provable reason.
This specimen breaks many of the “rules” that science has believed, such as the smaller brain capable of tool-use and other complex thought, the general size decrease instead of increase, and the time frame that it lived. We are forced to either re-think the way we see what we believe to be a nearly linear evolution, or we must believe that these are either a completely different species.
While the island effect had never been observed for a human, of course it can't instantly be discounted. But I find it difficult to believe that the island effect would take a typical homo erectus and cause the exact changes to it that would be needed to allow it to both fit with and have the same overall proportions as australopithecus. It would seem to defy the odds for this to happen.
Therefore I believe that homo floresiensis is a completely new species, and while may be a branch of our family tree as homo sapiens it is far distant. I think theses remains were maybe not a branch off our own human family tree but an entirely different class of creatures. I know this reason is vary fantastic but its my perspective.
I believe that with all the tests that were done trying to figure out where these fit into the overall evolutionary structure, the determination...