I could not find information on Archwiki before - search for BCM57780 redirects to
an incorrect page
Archwiki has the information OP found via reddit;
and a possible solution to order the modules in /etc/mkinitcpio.conf ;
and the modprobe option you found in Arch forum
Network configuration/Ethernet - Broadcom BCM57780 - ArchWiki
The modprobe option is simple with one command
echo 'softdep tg3 pre: broadcom' | sudo tee --append /etc/modprobe.d/broadcom.conf