Can someone explain bridge mode?

Got an Eero 6 pro with a Frontier install. Don't need a router since I have my own but I can't seem to pull an IP with my router. Frontier support is completely useless.

I can get an IP with the Eero. So I figured I'd put it in bridge mode and use my router behind it.

I put it in bridge and my laptop, connected wirelessly, gets the public address, not the router wired to the second port.

Is this the expected outcome??

Not really useful as a bridge.