1. The problem exists ( and is a genuine problem that quite a few people care about! ). 2. A good solution has not been found yet. ( also kind of good for you! ).
Apart from this, it also gives you a lot of information about the industry. Especially the discussions that are happening here. So, why dont you consider this a loooot of great feedback and go back to the drawing boards and go disrupt this industry ?
Don't get discouraged by a guy explaining why it can't work according to its theory.
20% retention is neither good nor bad. There are a lot of businesses that survive on one or two events a year. If you are in the business of selling metrics software (like his friend at MixPanel), you probably want people to come every day.
The "I don't have room in my brain" argument is just silly. I can open my refrigerator and see hundreds of different brands. There are millions of websites, of all kinds! Should we stop building websites because there are a lot of them and it's harder to differentiate?
It's pretty hard to swallow this kind of advice from a guy who founded a blogging platform in 2008, 5 years after blogger.
Anyway, as our man PG likes to say, just go make something useful. The rest will take care of itself.
As depressing as it sounds, there's little point in continuing product development without solid validation. Its a problem I ran into at my previous startup - a good product, but just not needed by enough people.