> A lot of firmware dev iteration seems to be build -> flash -> watch serial connection for debug prints.

Serial port? Maybe for the fancy folks. Us lunch-pail types would find an unused GPIO, blue-wire an LED, and blink out a code of your choosing.

Okay, I never actually had to blink an LED but it was in my bag of tricks. The real golden-ticket to debugging embedded devices was a development kit with JTAG. JTAG, coupled with expensive additional hardware and equally expensive software license, gave you a gdb-like interface for debug. Breakpoints, stack traces, all the good stuff you take for granted when working with Windows, Linux, or those ugly abominations we call web browsers.

Emulators were also a thing, especially if your product had a custom ASIC and you needed pre-silicon development. But I didn't use them a lot myself and it seemed like by the time you had your emulation environment setup, there was 1st gen silicon and a debug board sitting at your desk.

I'm not a firmware dev but the one's I've seen working usually have all sorts of fancy test kits, debug instrumentation, Software (chip scope?), etc. to debug with, not just relying on print debugging.

Not to say it isn't a valid way to debug, but there are definately better options available.