AAISP supplied my VMG1312-B10A with a slightly modified firmware (bug fixes that later went into the mainstream) pre-configured by them in router mode using my (live on Plusnet at the time) HG612 as the modem. (The strange reason given when I queried why being that was to correspond with my existing historical setup
I didn't like its WiFi so after a bit swapped it out for my ASUS RT-N66U.
A while later when my HG612 died I changed the Zyxel to modem mode (not easy at the time) as the instructions were basically how to convert it from modem/router to router! Even the definition of "bridge mode" meant the incoming WAN signal was from modem rather than a phone line! Then fed it into the ASUS.
I found an immediate increase of 3Mbps from around 50Mbps on the HG612.
My broadband basic info/help site - www.robertos.me.uk.
Domains, sites and mail hosting - Tsohost
Connections: OnePlus 8 Pro max 165Mbps down, 24Mbps up on Three, and B311 4G, tbb tests normally 35-45Mpbs down, 65Mbps off-peak, 9-24 up.
To argue with mindless bigots is foolish.