I basically agree with him, while have some differences in specific.
For DPOS, monitoring witnesses and removing bad or lazy witnesses are very important. In this sense, 100 seems too big to make dynamics in the top active witness list. I think around 30-50 is a good number.
As he said, 30 votes can make the witnesses dependent on few whales, as Steem is now. A further problem is 30 is too many for individuals to evaluate and monitor witnesses. The bigger the number, the psychological burden will exponentially increase. 1 is good number too, but I personally prefer 3-5, which is similar to the number of "very close relationship".
Well if you are not using all of your 100 votes, you should delegate that power to someone who is. Plain and simple.
That can end up with the concentration of power.
This is the drawback of DPOS. The 30 limit also imposes a concentration of power. It ultimately depends on the scale of the network.