[decisiveness]

Never rely on your ISP to provide great wifi equipment. This is not something specific to Comcast. Generally, it seems residential ISPs are only on the hook for providing quoted speeds via a wired connection to their gateway.

This is why I always either disable the wifi from my ISP's modem/router combo and branch off my own wifi router from the modem's LAN or request a modem only device from the ISP and use my wifi router's LAN. The downside to the former case is that your wifi devices are now double NATed (unless you use a wireless bridge) which can be annoying if you want to forward ports (you now have to do it twice). The modem/router combo might not support disabling its LAN to act as a bridge very well.