That's pretty much true, but I have to nitpick a bit. Arduino tends to mean an 8-bit AVR chip, say ATmega328. That's actually not very low-power and things get difficult once you need just a tiny bit of performance.

Luckily there are alternatives so you can choose the right tool for the job.

Yeah, the most common boards (cheap Uno/Leonardo clones on eBay/Aliexpress) are AVR, but newer Arduino boards (M0) are based on Cortex-M cores, and there's things like the ESP32 that can be used with Arduino IDE…

Absolutely. I see nothing but benefits from having both options (incidentally was thinking PIC due to power requirements) for a project. But the "hmmm" thought was about complexity of a system as time goes on. Was imagining dozens of unpatched Linux-based devices put on top of other dozens of devices in a system and the maintenance aspect took on a new tone.

It's like you can send an email with a single line of PHP code, which turns into 673 lines of system calls, which turns into thousands of assembly instructions and that's not even counting what happens after it's passed to a mailer - and at some point the complexity of being able to account for every action of a part becomes untenable.