He played an insignificant parts compared to the large incompetence shown by the team that decided Python's 3 feature set and handled the transition.
In general, whoever decided that such few features (in the initial versions) and such lacklustre fixes should be enough to make people adopt an incompatible version of the language.
They still did it better than the Perl people, so there's that.
It's Python 3.3 where migration started being a serious matter of discussion, and 3.4 added more 2.7 syntax backports to help the transition. And the community did follow on that. 3.3 and 3.4 are where many 2.x libraries added Python 3 compatibility.
Calling the Python core devs incompetent for something where instances of prior art can be counted on the digits of one hand that may have lost a few fingers is a bit rich.
I attended pycon a couple of years ago and was still new to python. I had (tried to) read "Learn Python the Hard Way" as well. I attended many of the "newbie to python" tutorials while at the conference and many of them had this book as a suggested read. I promptly informed the tutorial leaders how the latest version instructed people to never install python 3 and spoke ill of it as if ignored, python3 would just go away (note the tutorial classes where all in python 3). Most people seemed shocked by this but they all removed the recommendation for the book.
Flame me all you, but I was trying to jump ship from Perl (which (un)fortunately didn't really work as years later I still make most of my money from Perl stacks). And the last thing I wanted to jump from was one language that had a giant rift in the community (perl5/perl6) to a "newer" "better" community that had the same rift in it as well. Thankfully people seemed to come to their senses over the last couple of years and have started to throw out their python 2 code.