The incontrovertible evidence is worldwide platinum concentration spikes, coupled with soot from continent-spanning conflagrations, without corresponding sulfur fluctuations. Read the linked paper. It is solid. The people calling it cranky have been caught doing all kinds of shenanigans, such as calling melt glass spherules "pollen" without ever looking at any with an electron microscope, and sampling cores at the wrong places, carefully straddling the actual date.

Scientists can be as petty as any pol. The Wikipedia page is "curated" by one of those, a retired historian with no background in geology.