In several places I'd say you tilt your probability estimates in the most favorable direction to your argument. For example, you underestimate how much evidence the meteorite would give - 1/100th of the earth's surface destroyed every 1000 years is far too much. There have been 0 humanity-wiping-out events so far, over 1 million-ish years, this does not work out to P=10^-5. In estimating based off of expert opinion you load the intuitive die with "the calculations say" rather than "the physicist says"; calculations are either right or wrong.

I agree that the estimate of 10^-22 is likely too low, but I have a negative reaction to how you're arguing it.