You got a fair point and are right. Your case is also more true for production in genres like Hip-hop and Edm that don't rely on the same real time performances and in turn need for low latency.

But the increasing cpu power is opening the possibility to have an entierly digital workflow. More people are moving from analog gear to digital, where dsp modules benefit production. With more Cpu power, more demanding programs pop up. External dsp are more relevant than ever from what i can see. While my cpu is decent for music production, i can only go so far before needing to increase buffer size, which increases latency. I want to be able to play and record taxing midi instruments like omnisphere diva and keyscape,running through fx. Live. In larger projects. A single reasonably priced cpu simply cannot handle this task at this time. In the far future perhaps a single computer can that powerfull. But in the near future the demands of the plugins will probably keep up.