Hold up!
That's true but also not true... confused?
(I feel like I'm channeling Jerry now). So Google wifi gives your devices IP addresses in a range that NO other router does. One of the reasons they want you to use is as the only router is to avoid IP address conflicts and also maximise the bandwidth that GW gets.
But if you connected all you devices to GW then it will do the job for you with no conflicts and no messing around with the network settings required.
(To put it into perspective I live in the UK; I have Sky broadband and sat TV. The Sky system is a mesh system itself that streams the satellite signal around the house. When I used my AirPort Extreme with it I had to put the AE into bridge mode as the IP range was causing a conflict. Not so with GW. Simply plugged it in and connected all wifi devices to GW. The sky boxes use its own network to stream TV and the GW if for everything else. No issues or conflicts).
(Actually one tiny thing; I cant access my Philips Hue on.here GW control on my iMac but I can on every other device so it isn't a big deal. Hue works on Google Home, Amazon Echo and HomeKit.).
The chances are unless you have some super complicated system it will work great. It is correct in saying you can't mesh GW if you put it into bridge mode but as I just explained I don't see any reason you will need to change any settings.