Quality over quantity - and if prices indicate anything it’s a more efficient approach. Battery building is also limited to lithium availability, so there’s many more cars you can convert if you put 1/5 of the battery in each one. Fuel is much more energy dense than batteries so the removed weight is making the car more efficient as well. Ultimately I think it’s important to value flexibility and maximizing tradeoffs, which I feel plug in hybrids achieve.