Google has no need to collect any traffic data from WiFi and it doesn't. They get plenty of information on its users from all the other services people willingly use and opt into. You can opt out of all the data collection methods via the app.
App-based management makes use of the fact that phones are something we all have now. It also enables two-factor authentication, which, unfortunately, only eero takes advantage of now.
The requirement of cloud services has both positive and negative points. It enables easy remote management and the application of more analytic horsepower than is economically feasible to include in reasonably priced products. It also allows machine learning over thousands (millions?) of networks to tune algorithms. The negative is that if the company goes belly up, your device is bricked. But this is a general technology issue not restricted to routers.
Ya pays your money and ya takes your choice.
