My understanding is that V2G (vehicle to grid) requires transfer switches etc to be installed to your home electrical setup so you don't accidentally backfeed electricity into the grid. So it's never going to be a simply a matter of getting a better EV.
Why exactly do you want a backup? If you're looking to maintain a few key appliances or internet during a grid outage a vehicle with V2L like an MG4 or BYD might be sufficient.
You probably already know this, but for the sake of providing context to other readers: V2G - vehicle to grid, providing power to the grid from your car battery like is common for home solar batteries; V2L - vehicle to load, a power outlet using energy from your car battery.
Transfer switches are trivial to have installed. I already have a manual, interlocked one for a portable generator.
I have a 13kW array on the roof and live in a place where ice storms make power outages a thing most years. My solar inverter is grid following. Even if I can't get grid forming from a car I'd only have to pay for a small battery and grid forming inverter to cold start the whole operation rather than $10K of extra batteries for them to do the grid forming. Then I can let the solar and vehicle do their thing and follow the islanded grid during the outage.