I believe the main question here is that whether they were doomed without asteroid regardless, and in that sense we can’t blame asteroid alone or primarily.

Oh, yes, the point on the asteroid alone is possible, but a mass extinction at the same time an asteroid nearly destroys the wold being mainly caused by something other is a hell of a coincidence.

Not actually that big of coincidence. We tend to forgot the scale of these things. I remember reading that dinosaurs were already in decline for 2-3 million years. So if asteroids like that hit once per 100 million years, odds are not that small. Maybe 3% give or take.