You can certainly do a lot even with low end CPUs in automation (and they are certainly used a lot there).
But there's a lot of basically-desktop CPUs in industrial automation too, because those are not that expensive and very useful for higher bandwidth interfaces (think ethernet based), cycle times in the microsecond range (higher CPU clock gives you a much more generous cycle budget) and just a generally easier time doing anything where a FPU and memory helps (motion planning, driving some UI on a touch panel, etc).
But there's a lot of basically-desktop CPUs in industrial automation too, because those are not that expensive and very useful for higher bandwidth interfaces (think ethernet based), cycle times in the microsecond range (higher CPU clock gives you a much more generous cycle budget) and just a generally easier time doing anything where a FPU and memory helps (motion planning, driving some UI on a touch panel, etc).
See:
https://www.beckhoff.com/en-en/products/ipc/embedded-pcs/