In any case, you can always throw more CPUs into your box, so in the event that individual CPUs stop getting better then they can start shipping boxes with dual or quad CPU sockets, or even cards with grid processing on them.
I'm not gonna argue that point, but I figured that I'd share this footnote in computing history, since it did actually happen at least once in the consumer market. Same thing happens in servers too, but that's just boring.
Introducing: the
Quad FX! This was a platform which let you insert 2 Athlon 64 FX's into a dual socket motherboard. Since these chips were dual-cores on their own, the idea was that you could get a quad-core system by putting two of them into the same system.
2nd half of 2006. AMD were caught off guard when Intel annnounced their Core 2 Quads, so they had to act quick. They had 2 options: make quad-core chips on their existing 90 nm process (wouldn't work; too much heat output) or wait until 2007 (and risk losing mindshare/relevance when those
do come out, at least in AMD's head). So they took the third option: mount two Athlon 64s on the same motherboard, and now they get a quad-core of their own to beat Intel with.
In theory, anyway. I mean, it was a quad-core, but the problem was, it sucked. AMD's aging K8 architecture just couldn't beat Intel's Core 2 architecture. K8 may have beaten Netburst, but Core 2 was just such a good architecture that descendants of it are still used in Pentium Gold, i3, i5, i7 and i9 processors. And even if it could beat the Core 2 Quad (which it didn't; pick any workload, and it usually got its ass handed to it), this is literally running 2 processors in a system at once. You'd consume double the power of a Core 2 Quad, and for what? A power hog of a system that didn't even touch the processors it was meant to beat.
In the end, it was a market failure. AMD released their Phenom line of chips in late 2007, but Intel still remained the performance king. Intel's dominance in the CPU space would continue until around 2017-2020, where AMD's Ryzen chips are finally starting to be competitive with, and sometimes even beat Intel.
(I'm pulling most of my info from an Anandtech review of the Quad FX:
here it is)