I see what our problem is. You are viewing extinction as an event, while I am viewing it is a dynamic process. For example, we once had millions of passenger pigeons. Then we were down to a few individuals, but apparently they needed the excitement of masses to stir their reproductive hormones, so that once they fell below a critical number, they were essentially extinct even though some were still alive. So for them there was an extinction process, not a single extinction event. For the same reason I believe that the end of the dinosaurs was a process rather than a single event, but the end result was all dinosaurs died and relatively quickly as goes geologic time.
Extinction comes from the end of the life of the last of a species, it’s not a “process”. Species in human times can be on a manmade endangered list, but they aren’t extinct.
The dinos were completely wiped out. While there are fossils spread out over 135 million years or so, there are none after the K-T boundary. So they didn’t dwindle down for other reasons, then there was coincidentally an impact that had nothing to do with it. Nor were they in decline for millions of years (another foolish idea) and were finally tipped into the dustbin by a sudden uptick in volcanic eruptions.