We first started talking about SMTs after Dan left. In that time, he fund raised, engineered and built EOS. We haven't accomplished much in that time.
I think he was already working on it before he left, certainly design if nothing else but possibly code too. He made a number of posts about building smart contracts on Steem, and that included reporting on having implemented some code to the proof-of-concept stage at least. Also, there was a reason for that whole dust-up over making the Steem code open source without management approval that happened right before he left (days, IIRC). My guess is that he already had large parts of the EOS design built on top of the Steem code mapped out, if not already implemented and needed the license change so he could use that work on a new chain.
Anyway your point on relative rate of progress is valid. It applies equally to other blockchain projects with well-functioning development not just EOS.
RE: Real Talk: The Future of Steem