Oh well. I think it is often a problem running into a help- and clueless hotline/email person that doesn't know shit and is scared of that strange L-Word. So they block it with a copy and paste "blahblah" lame answer. Then, a lot of stuff lies in the hands of the BIOS Vendors themselves (see agd5f's post here).
I personally use pcie_aspm=force and it seems to be ok. Still, we really need that secret password to reach the better informed hotline.
My experience: I called a few times hotlines when I really ran into a problem I couldn't seem to fix on my own but that person was normally 100x more clueless than I. One of the few exception were a now defunct internet provider (but really depends whom you reach in the callcenter) and iiyama (the monitor folks).
Especially with mainboard vendors it seems that they have one single support person that barely speaks English and is overloaded with support request from the whole world. Often they just send you pre-compiled blahblah from the FAQ not even having actually read your question. Sad thing that support is often so lousy.
Can't tell about Gigabyte since I didn't have one but I checked their webpages from time to time and afair they had this "Linux users pls download drivers from chipset manufacturer" and iirc. they provide a BIOS update mechanism that enables you (like ASUS) to put the BIOS image to a FAT32 medium (floppy, HDD, stick) and just load it from a small program "inside" the BIOS setup. No DOS or Windows required.
And when it comes to boards I guess a lot is just
a) chipset from AMD, intel or nv or whom ever
b) additional network chip (Realtek, via, something)
c) audio chip
d) USB3 from Renesas or NEC if not in chipset
e) firewire from via
f) SuperIO from e.g. ITE or Fintek
... whatever I forgot.
But all compiled mainly from "standard" components without much own input.