As far as measuring the sort of thing people are talking about:
How has your Net Promoter Score changed? Do you do surveys with questions like, "How disappointed would you be if Stack Overflow went away tomorrow?" How does attrition of users with at least 3 upvoted answers look over time?
I wouldn't expect the metrics you mention to capture the sort of user satisfaction issues, and I could see the above numbers not showing a problem because general growth is masking specific issues. I'm sure you can name quite a number of products whose quality decline started well before popularity peaked.
He provided no evidence. Do some science, don't waste everyone's time with unsubstantiated opinions.
That's actually what Stack Exchange is about, so it's not surprising I guess that there's this impedance mismatch. If you want to just have a bunch of opinions, take it to Quora.
So you get to set the rules for what appears not only on Stack Exchange, but some guy's own blog? I'd love to see your explanation for that.
If you want to see if he has evidence, try asking him. And not in a "it's your job to argue with me" way. Call him up on the phone, ask open questions, and then listen to the answers without being demanding or dismissive like you are here.
That's a pretty basic product management skill. If it's something you're not familiar with, plenty of people teach classes. I know the Luxr folks do a good job, for example.
How has your Net Promoter Score changed? Do you do surveys with questions like, "How disappointed would you be if Stack Overflow went away tomorrow?" How does attrition of users with at least 3 upvoted answers look over time?
I wouldn't expect the metrics you mention to capture the sort of user satisfaction issues, and I could see the above numbers not showing a problem because general growth is masking specific issues. I'm sure you can name quite a number of products whose quality decline started well before popularity peaked.