Couldn’t you try a double NAT? then put the 2nd router in a DMZ?
Would that work?
Probably, but I imagine it wouldn't be without issues, potentially some frustrating ones as I want remote access and run a number of services. Modem mode is offered in earlier versions of the hub, so obviously DMZ and double NAT isn't the ideal solution I suppose.
I think with that setup I'd also encounter some of the performance issues with the router still (e.g. bufferbloat, occasional drop-outs) or perhaps I could mitigate them with my own hardware - not sure. Don't have the time to explore it or troubleshoot it, especially as it would be on the edge or outside my expertise to fully understand.