The lack of creatures with appendages suitable for tool wielding or the evident brain capacity for the task doesn't come into it just a tiny bit?

I'm not exactly sure how much more or less common fossils are from various time periods but I think its fair to point out we have very few skeletons of certain hominids running around that fit that description in East Africa a few million years back.

Which dosen't change that you are right that it is very very unlikely to be the case that a tool using or very clever undiscovered species (at least to the extent needed to make the argument work) existed then. But we should keep in mind just what a puny fraction of extinct species are known to us.