There's room in the market for both of these types of vehicles. Asking people who typically buy big luxury cars to 'just buy a smaller car' would be nice in theory, but isn't going to happen in practice. There are many reasons, valid or potentially invalid, to own a larger car or a truck, and often you're not going to change people's minds on that.
But, no, that's not right. If someone is typically a buyer of a ... Range Rover, or a BMW X5, or something like that, then replacing that car with an EV of equivalent size makes a proportionally larger impact on the environment than someone who replaces their Corolla with a small EV.
Small 2 cycle engines like mopeds are the biggest contributor. Then small cars, these luxury cars are a small percent of global emissions.
Also, those people don't have to drive big luxury cars, they can buy these smaller cars.