Filp over to things like math performance running C and there's no contest. ARM wins.
not really, unless you count FPUs and use faster clock speed - not a fair fight then, in my view: I think I did an extensive dhrystone benchmarking of mcus, from 8051 to CM4F. No significant advantage for CMx chips over other comparable chips. PIC24 and PIC32 did reasonably well while CM0 and some CM3 did poorly.
All PIC32MZ EF have single cycle FPU (single and double precision) and DSP instructions. M4F is only single precision. M7 has two optional FPUs, either single or single+double.
Before PIC32MZ is written off, in terms of hardware while I agree that the original EC version is indeed something to avoid, the more recent PIC32MZ EF is definitely worth consideration if you're at that segment of the market (M4/M4F/M7). The EC was simply not ready for release.
On another note regarding whether or not to be price conscious, while I agree for one off's and very short runs, say 20 or less, you're wasting your time trying to shave off a few cents here and there, that's not the case for larger volumes, even from 100 off. Part of the hardware design criteria has to be pricing and availability of parts in the latter case, and you have to look at it in terms of a system, not just the individual parts. For example adding a reasonable performance ADC to an MCU can be a much more expensive piece of work than finding an MCU with that ADC integrated into the chip, you may need external FIFOs and muxes too for example.
Whether ARM or not should not just depend on the core. Realistically, knowing ARM from one manufacturer isn't going to help that much when going to another. More important is the already accumulated knowledge of toolchains and a given manufacturer's devices. Learning a new device from a different manufacturer, with or without ARM, is still going to need work, and the core is a relatively small part of that.
Having said all that, if you're just starting out in the MCU world and it's only 32 bit you're interested in, and don't care about anything else like peripherals and toolchains, I'd have little hesitation in suggesting that ARM is going to be a better choice due to sheer market penetration. Your biggest problem then is understanding the ARM market and the differentiators, which between ARM and their licensees' marketing have done a crap job over the years.