Ask HN: Decompiling Firmware – Best Practices

I have a number of ROM images for embedded processors, mostly 8 bit ones. The code was most likely written in C. My goal is to completely decompile to source code (comments optional but if something is recognized, sure) so that I can add functionality, recompile, and use. I have been using Ghidra and IDA free but there is still an enormous amount of manual work needed, like hundreds or thousands of hours and mostly and C code is nearly useless and I've gotten my understandings from looking at the assembler outputs. Is this the best that can be done? Can GPT-4, either on its own or in conjunction with either of the tools I use do a better job? Because right now I'm kind of stuck doing manual patches and sometimes just jumping to a blank area to put new code which kind of sucks.