I’ve ridden ebikes with 36v and 48v and based on experience those with 36v are just less responsive, especially wheyoubafd some weight , a 5lb lock, a spare battery , a 15lb backpack.Are you assuming it to be sluggish because it's 36v, or do you know it to be sluggish due to reviews and/or a test-ride?
The reason why I ask is a more efficient motor can do more with less. The upgrade from Shimano STePS 6000 to STePS 6100 brought with it a 20% increase in torque and a 25% increase in range on the exact same battery. To me, you want the lowest voltage/wattage/amperage motor you can get that will do the job because, all other things being equal, that should reduce weight, reduce cost, and improve range.
Put even more simply, I'd take a 10w LED lightbulb over a 60w incandescent lightbulb any day. It's not about how fast the unit can drain power, it's what it can do with that power.
I share your surprise about the downgrade in battery capacity for many of the 2020 Giant e-bikes, so I agree with your conclusion. I'm just curious about elements of how you got there!
It may be responsive for a lighter person put a 215lb would not like it.
If the same ebike had 48v system the 215lb rider would buy it.
I didn’t rode the new Giant.
The other e road bike Specialized Creo at 6.5k is sold out....
Most e bikes maybe 90% of them have a 48volt system.