Mammals and Chicxulub

At https://www.sciencedaily.com/releases/2025/04/250401233454.htm … mammals were already living in numbers prior to the event which killed the dinosaurs. The latter, of course, survive into the modern world as birds. Therefore it was likely that mammals were relatively well attested during the dinosaur dominance of animal life. Why not? If mammals existed  in substantial numbers, living in less conspicious parts of the environment, that would  amount to the spring board required for them to expand and fill in the niche left behind by the mass kill off the lumbering beasts. A less strict version of Darwinianism is probably long overdue. Actually, that is probably true from the perspective of scientists – but less so from the perception of the public at large.