No, that was not the case. You do not seem to understand what that means. It only means that the same physical laws in existence today existed in the past. A large asteroid would be disastrous at any time. I think you are putting your own spin on this.
Again, no. It has always meant that the physical laws were the same then as now. That is all. From that we can deduct what happened in the past.
It seems to be one of those days.

In my direct experience "The Present is the Key to the Past" did not simply refer to constancy of physical laws, but constancy of the expression of those physical laws. Bombardment was off the table. The extinction events were seen as gradual affairs. Most were not even recognised.
On the subject of deep sea fossils I omitted the more obvious instances. I can only put that down to thinking after midnight.
Here is an example. I draw your attention to the last paragraph.
Grimes and Crossley
A diverse ichnofauna from silurian flysch of the aberystwyth grits formation, Wales Geological Journal Vol26 1991
Abstract:
The most extensive ichnofauna yet recorded from a deep water Lower Palaeozoic sequence occurs within the distal turbidites of the Lower Silurian Aberystwyth Grits Formation of Central Wales.
The strata contain an abundant assemblage comprising 25 ichnogenera:
Asteriacites, Bergaueria, Chondrites, Cochlichnus, Cosmorhaphe, Glockerichnus, Gordia, Helicolithus, Helminthopsis, Helminthoida, Hormosiroidea, Lorenzinia, Megagrapton, Monomorphichnus, Neonereites, Nereites, Palaeophycus, Paleodictyon, Planolites, Protopaleodictyon, Spirorhaphe, Spirophycus, Squamodictyon, Subphyllochorda, Taphrhelminthopsis; 36 ichnospecies are described, three of which (
Asteriacites aberensis, Helminthopsis regularis, Cosmorhaphe elongata) are new.
The inorganic sedimentary structures and trace fossils of some 418 sandstone beds were examined in detail; 16 per cent of the beds commence with Divisions A or B and 84 per cent with Division C of the turbidite sequence. This indicates a relatively distal environment, mainly receiving low velocity turbidity currents, and favouring trace fossil preservation. The most common traces were
Helminthopsis, Paleodictyon, and
Squamodictyon which were found on 46 per cent, 34 per cent, and 19 per cent of the beds examined.
Data from this, and other recently described sequences, confirms that there was a gradual increase in trace fossil diversity in the deep oceans throughout the Lower Palaeozoic, in contrast to the situation in shallow water shelf seas where a peak was reached as early as the Lower Cambrian.