I think this the the point -- that in general someone who is not in a PhD program generally won't spend such a huge amount of time focused purely on a very narrow but deep problem.

There are obviously exceptions to every rule, but I think this is a good point. Most folks who are NOT in an academic program don't take out loans and stop work on all practical projects for 3-5 years to focus like this.

I'm not very familiar with the CS PhD world -- I'm very much in the self-taught category, personally -- but I'm married to an author who got a (fully-funded) MFA in creative writing. It was great -- not because the profs were teaching anyone how to write (if you didn't already know, you didn't get into the program), but because it gave her a couple of years out of the real world, focused entirely on her writing, surrounded by very supportive & similarly focused people.