The author seems to paint a broad brush in saying all dynamic languages are poorly designed. Languages can have different design goals.
From Matz, Ruby's creator;
> Instead of emphasizing the what, I want to emphasize the how part: how we feel while programming. That's Ruby's main difference from other language designs. I emphasize the feeling, in particular, how I feel using Ruby.
( http://www.artima.com/intv/rubyP.html )
So one of Ruby's primary design goals was programmer happiness, and in that respect it isn't not poorly designed at all. The technical 'perfection' of a programming language only matters to a point, it's us as programmers people that have to speak its language all day, and optimising for how we feel doing it is a valid design goal.
I don't think it is a valid criticism to say something is poorly designed, without looking at its design goals. Every language is poorly designed in one way or another.