The silly thing was releasing PS4 Pro and the whole iterative console concept.
Disagree. People currently expect new versions of devices to have more improvements than just size. It would have been silly if there was a lack of game compatibility but that wasn't the case.
PS5 in 2018 makes a lot of sense.
It honestly wouldn't make sense to me regardless of the PS4 Pro. The PS4 is currently swinging with many games and many developers comfortable with using the system. Cut off its peak period instantly just to release the PS5? Really silly -- especially (again) with the PS4 Pro. It would cause many to wonder when the right time would be to upgrade since Sony would have released multiple consoles/versions in such a short span of time.
New phones can release every year because people NEED phones. They are tools. People don't need game consoles at the point in which it would make sense for a company to release a new $300-$400 box every two years or less.