A 52 watt hour battery is very middle of the road. The tradeoff you're making is aluminum for plastic. The aluminum MBA is heavier and feels more premium. Plastic is an underrated material IMO -- in many situations it will bend rather than break.
note that it's a 66.5 W・hr battery. aluminum is pliable too.
Most of the weight is the aluminum and not the battery.
but the ability to affect weight is mostly in the components, and the battery is the largest and heaviest of these. aluminum is pretty light but you need a certain amount of it to have the structural characteristics they're aiming for.
The 13" Ryzen 7 5700U LG Gram weighs 980 grams with a 51 kWh battery. The 13" M2 MBA weighs 1200g with a 52.6 kWh battery. The main weight difference is not from the 1.6 kWh of battery but the choice of aluminum over magnesium alloy. I'm sure things will be similar for the 15" MBA vs. 15" LG Gram.