Genesis is patently absurd if taken literally. THAT much at least was made clear in the Scopes trial, in the infamous dialogue when Darrow put his opposing lawyer, WIlliam Jennings Bryan. on the stand and forced him to testify as a biblical expert.
I don't know about monsters -- the chances of that many genes changing all at once is pretty slim. The model that makes sense to me is gradual cumulative change which is continuously vectored toward workability by ordinary survival pressures. I'd like to see an explication of this notion of sudden large change speciation.
Re wide-scale extinctions, one difference it made, for example, when the dinosaur families collapsed was that several species were able to shift from nocturnal to diurnal operations. One result of this was the recovery of the third cone structure in the eye in some cases where it had been bred out through generations of nocturnal living. Dawkins discusses this in "The Ancestor's Tale".