Well I guess that's down to
(••)
( ••)>⌐■-■
(⌐■_■)
your opinion.
YEEEAAAH
Memes aside, I think it's true that what is an opinionated question is, in itself, an opinion. For the most part, if enough people flag a question (4), there is usually cause to hide it.
I should also point out that "What are all the derp Pokemon?" was asked more than 3 years ago. In that time, I think we've changed our attitudes to opinionated questions on this site, and have got better at saying, "that's too opinionated, there's no one answer to this question".
That said, I don't think the problem with your question is that it's too opinionated, but too time consuming to answer. Your question means that the person answering has to go through all the Pokemon games, trawling through the dialogue of 24 games to provide a sufficient answer.
As for "what are all the derp Pokemon", I guess it's just shows how the site has changed since 2012.