In most of the target applications of these chips, you'll typically have a couple of real-time tasks. This will run on a dedicated core, or in kernel space, or with Xenomai. The rest will be firmware update services, telemetry, and maybe Bluetooth or a web GUI. Stuff where the execution speed doesn't really matter, as long as it's "fast enough". Armv7 is more than sufficient for that kind of thing.
The STM32MP2 family will probably replace the MP1 once it's in full production, but that doesn't mean the MP1 is a bad chip to use in new designs today.
The chip's competition is NXP's i.MX line of parts. If I got a good price from ST on it (and a production guarantee), I'd consider using it in a number of new products, even though the main CPUs are 32-bit Armv7 cores.