An average router ruined my smart home, especially my Nest speakers

In retrospect, I should have learned my lesson the first time. For the past year, I have been adding some smart home devices to my apartment and seeing their performance drop with each passing minute. I blamed the devices — especially my Google Nest speakers — instead of the router because I was on a fiber connection and getting 500-600Mbps speeds on my computers and phones, so how could it possibly be the router’s fault? Well, it was the router’s fault. But let’s back up.