I've addressed this in previous posts.
Not sure where to start with "Matthew Collins, A-Letter Editor", who either doesn't seem to be very experienced or is just interested in promoting a bear agenda.
P/E ratio is not a "complicated" concept nor does it have an endless amount of assumptions. Price is easy to understand..
As for earnings, the time period is typically one year forward OR LTM earnings. There is nothing complicated or "cooked" here really either.
If the number does not include write-offs from financial institutions, it is normally noted. Interesting that in an effort to either make things "simple", or to just promote his agenda, the author does not specify whether his forward number includes write-downs or not.
I've never seen someone calculate a P/E based on the "last couple of quarters". That's asinine.