The Asus RT-N66U was released on ‎December 22, 2011 according to Amazon,[1] and the last official firmware update was on June 18, 2020.[2] That's 8.5 years of support (assuming no future updates) compared to the OnHub's 7-7.5 years.
More importantly, the Asus RT-N66U is still fully functional and still supported on the Asus Router mobile app.[3] Unlike OnHub, Asus routers that run on non-Google firmware have a web interface so the network settings will continue to be adjustable even after app support ends.
Older Asus routers, including the RT-N66U, tend to be supported by open source firmware like DD-WRT.[4] OnHub is not.