It's not random. I get how comparing a pitcher from 2015 with the same pitcher in 2017 is fraught with problems, but I have done year by year- same pitchers- same years- 2-3 catchers. True, there are other variables at play, such as who was the opposing line-up and what field were the games played on with one catcher vs the other, but when you do a study based on 5-6 years and nearly every year shows vast disparities all in one direction, I think one can determine the trend has to do with something one catcher is doing better than the other.
To say there is zero effect from one catcher and another really blows my mind. Sorry, it just does.
I can see you and others thinking I value it way to much as "mind-blowing," too, but I will argue that just because I talk about it a lot does not mean I think it is the most important thing a catcher brings to his overall value.
I do sometimes wonder, if a 1.50 ERA disparity is indeed linked totally to the catcher's CERA related skills, I might actually be understating it's value to certain pitchers - not all pitchers, of course.