The reason for dividing the workload across several Arduinos was due to their limited processing power.
Nooo. A tenth of a ms (100 µs, 1600 instructions) is a very long time even on an AVR. Write the software properly and one would be just fine.
Not so long ago most 3D printers were controlled by AVR Arduinos, controlling the timing of individual stepper motor step pulses to X, Y, Z, and extruder stepper motors, running a PID control algorithm for the extruder heater, calculating acceleration profiles for the X and Y steppers, measuring the temperature, AND receiving and interpreting the G-code stream of commands, and often displaying status on an LCD.
A Mega2560 was used in order to have enough pins, and enough code size, but it was no faster than the CPU in an Uno or Pro Mini.
A better reason to use multiple MPUs would be to put them close to what they were measuring to reduce signal integrity issues, while having the logging communications over a channel with error detection and retry.
You might also want/need a dedicated one to write the SD card, depending on how long writing a sector takes and whether it can be interrupted. TBH you'd be better off using a hardwired SPI flash chip, and then have a mode to dump its contents to an CD card (or out the UART or whatever) after the ride.
But, yes, technology has moved on.
For the last five years I'd say the go-to device for your needs would be the $25 or so Teensy 4.0 (or 4.1) board, with a 32 bit 600 MHz dual-issue Cortex-M7 (close to 900 MIPS and they're 32 bit MIPS), 1 MB RAM, a lot of GPIO (including analogue) pins. And it runs Arduino sketches with a fantastic OOTB experience -- I had mine running blinky in about 3 minutes flat.
As an example of the performance, on my personal primes benchmark [1] a Teensy 4.0 took 43.5 seconds at its default 600 MHz, while a 20 MHz ATMega2560 took 13449.5 seconds, a factor of just over 300x.
Ok, so that's 2019 tech.
My go-to now is the $3 Milk-V Duo. It's got not 1 MB RAM but 64 MB, has a 700 MHz "microcontroller" core *plus* a 1 GHz (actually the default software runs it 850 MHz, but w/e) core running full Linux (typically Buildroot for the user-land, but you could put Debain/Ubuntu Server etc). It's got 26 GPIOs (only 2 ADC capable, sadly). And you can run Arduino sketches on the microcontroller core at the same time Linux is running on its core.
https://milkv.io/docs/duo/overviewI don't know the exact times off-hand, but either the Teensy 4 or the Duo should be able to switch threads in an RTOS (or Linux for the Duo) in well under a µs let alone a ms.
Heck, I'd think an AVR could switch threads in under 10 µs.
[1]
https://hoult.org/primes.txt