To be clear, a retcon stands for "retroactive convention," the key facet of a retcon is that it changes something about a part of the story that has already happened or the fictional world's history and asserts that it had always been that way.
There's a fine line to be argued within that about say, revelations over someone's past as a part of the story versus the same as retcon. It could be argued that Naruto being the son of the Fourth was a bit of a retcon as his treatment by the village growing up doesn't really track with him being a person of significant status, Jinchuriki notwithstanding.
However, not all bad writing is a retcon and not all retcons are bad writing.
Goku's characterisation and continuing decreasing intelligence in Super? Not a retcon, just bad writing.
The introduction of evolved Sharingan and elemental weaknesses into jutsu in Naruto? Again, not a retcon, revelation of new information that changed the story going forward but, critically, not backward.