There's wide variation in hardware quality, but consumer-oriented stuff is a lot more likely to have thermal issues and crappy power supplies.
For software, things are more uniformly bad. Almost every commercial router uses the drivers provided by the chipset vendor, and those are always bad. Even the poster child for open-source drivers (Atheros ath9k 802.11n) still had some nasty lockup bugs this year (eg. https://dev.openwrt.org/browser/trunk/package/kernel/mac8021...). The closed-source drivers get much less maintenance.
And then the router vendors have a team of morons slap together a web interface where all the priorities are on branding, and none on actually exposing the right functionality of the underlying Linux system in a secure manner. And that's if they're even using Linux.
OpenWRT makes an extremely powerful argument that the problems is the fragmentation of development instead of a single ongoing centralized project.
The jury's still out on where this effort from Google will fall. They've got some people who definitely know what they're doing (eg. Avery Pennarun, though I don't know if he's involved with this). On the other hand, core networking performance and stability clearly isn't what they're emphasizing, and they appear to be using the same ath10k hardware and drivers as everyone else.