It is “hard” science. Paleontology is the study of fossils including comparisons of morphologicaly similar fossils. Of course, over deep time, DNA comparisons are impossible. That doesn’t mean that observational science doesn’t exist.
I disagree that paleontology is hard science. It is too much subject to subjectivity. That is not a knock on the field, just it’s nature by dint of Nature.
As far as “Deep time” DNA comparisons, no, that is not necessary.
It would be comparisons of extant genomes. If their theory is worth anything, it should be able to predict relations of currently existing species.