Comparing different processor architectures isn't going to deliver the proper answer.
A Quad Core processor is going to be an effective solution for applications that can spread tasks across the cores and run them in parallel. Think of video compression apps or other apps that manage a large sequence of data.
Where Quad Core apps do not do well in is apps that have time sensitive data that is difficult to run in parallel and thusly will be constrained to one or two cores.
Today's Operating Systems do a good job of leveraging multiple cores while individual apps tend to manage two cores and begin to lose efficiency as the cores begin to increase from that point.
The reason why you are seeing more than two core systems increase is because with the smaller processes of today's CPU design it's easier to toss in more cores than it is to scale the Ghz up.
Many core is here to stay and so Apple and other software vendors are looking to leverage software to take advantage.
Unfortunately the A15's are probably not going to be ready for mass consumption until later this year, so we'll have to wait and see what kind of A9 apple decides to use
Unfortunately the A15's are probably not going to be ready for mass consumption until later this year, so we'll have to wait and see what kind of A9 apple decides to use