The VW Golf Mk8 might be a better comparison with an unloaded curb weight of 1255 kg, which reduces the gap from 543kg to 403kg.
(Note that for the gasoline and diesel cars, lighter trims give longer range, whereas it is opposite for electric cars, and that a fully loaded 45L tank of a polo weighs less than 40kg, especially if gasoline)
The lower battery trim is not available in all markets, and only does 300km on a charge which is below average. As such the minimum weight will have to be the 1658 kg value.
The BYD is taller to offset the battery, making the size misleading. However, the golf is not particularly a particularly good or space efficient car - others will do better at similar or lower weight.
250kg seems like a fair minimum weight increase, roughly 20%. The larger the car, the larger the gap though, as the rocket equation catches up - see a Skoda Octavia vs. a Polestar 2.
EVs are still way more efficient, but that doesn't mean we should turn our blind eye to making an already bad tire problem worse.
Same tier EVs are always more powerful than gasoline cars as they are generally just battery limited, not motor limited.
EVs are just a better tech in that regard, and buyers are not buying a Dolphin or golf based on torque or max HP. They're compacts in the same space. Someone looking at a dolphin would more likely be looking at the lighter eco motors.
This is true in other tiers too, e.g. a performance tier gasoline car might be 250-350 HP, while the same tier EV might start at 450-550hp just because they can.
The difference within a tier, simply based on the fact you're replacing at best a lightweight 100kg engine with 400-500kg worth of battery, can't be as small as you suggest.
With larger EVs, the battery weight is much greater, increasing the impact. Rocket equation and all.
BYD Dolphin weight 1600kg, length 4290mm.
VW Polo weight 1580kg, length 3971 mm.
https://www.automobiledimension.com/model/byd/dolphin
https://auto.economictimes.indiatimes.com/cars/volkswagen-po...