Whisper was pretty deliberately designed to usher in a new play style for Imperial players. Previously, Imperials basically had the TIE Swarm as their most viable archetype. And the only question you had to ask before Wave 4 was "how well will this list do against a TIE Swarm?" As a result of this, PS was not usually worth the points spent- non TIE Swarms would almost always be moving and shooting before TIE Swarms.
Because PS wasn't really worth paying for, upgrades weren't very much worth paying for. The common wisdom was that ships were basically disposable, so you should run them lean.
After the Phantom dropped, you needed to ask "how well will this list do against TIE Swarms and Phantoms?"
When the CR-90 dropped, the question became "How will this list fare against Swarms, Phantoms, and Fat Han?"
Btw: this isn't me talking, at least not exclusively. This is me paraphrasing Paul Heaver.
Some small rules issues gave undue preference to PS9 Phantoms and point Fotress Turrets. Those rules issues seem to have been smoothed out, while maintaining the integrity of what makes those ships fun and interesting to fly.
As a result of all _that_, Swarms, Turrets and Phantoms are all still viable. But so are a great many archetypes. In the current era (call it the World's 2015 era, so post-Nu!Core, pre-Gozanti) you need a list that's good against: high PS arc dodgers, hammer and anvil 2 ship lists, BroBots!, and still: Swarms.
Pheaver actually commented in his post-World's interview that he couldn't build a list that would be better than anything he would come up against. There simply wasn't a most-dominant arcetype.
This seems good and healthy. I am a tiny bit concerned that the only dominant arcetype Scum have is the BroBots, but they have lots of raw material that FFG can refine into a second and third archetype.