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.
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.