It is not preferences, it literally is about quality. There is a real incoherence and particular style of lazy art that is endemic to a lot of late '80s early '90s manga. City Hunter, Kenji
http://myanimelist.net/manga/15426/Kenji, not to mention that they all have the same protagonists and gags. Their modern inheritors are manga like, say, Ikigami or Heads or that one about a virus; it is slightly different, but the poor quality has just changed to be a slightly different art style (even worse, sadly).
The worst part of Conan and Kindaichi both is the unwillingness to have stories that are
not murders or murder attempts anyway, since the rates at which they happen, and especially happen involving the protagonists, is really hard to keep belief suspended throughout. In my eyes, better murder stories does not really help anything, but the style they are handled in Kindaichi is just plain sloppier, that is all there is to it!