This seems like just another opinion stated loudly with a link bait title. Even an anecdotal usability test with a handful of participants would go much further at establishing this argument than simply stating it as fact.
"Arrow icons are intended for disclosure affordances, but that should remain consistent for all arrow icons no matter which direction they point."
where is this rule coming from? are you sure users are aware of it?
Nope, the X is widely used in input fields to give the user a chance to empty the field instantly. This solution would be a major break, as most user would expect that.