I have the same issue but I think it's by design. I'm think of 2 reasons why is the reg braking so aggressive.
1. If you don't need to accelerate, the car will brake.... Because it's sport mode?
2. Sport mode is using a lot of battery for boosting so the car needs to regen as much power as possible in order to keep up. Speaking of this, does it happen when your battery is above 20% or above the minimum threshold that you set?
Considering Cupra compete in Formula E & ECTR, it’s likely they were going for a similar feel in their road cars under EV, as their race cars do. The
problem is that even in sport mode, Road driving rarely requires hard acceleration, followed by hard braking.
I asked the service desk when my car went in the other day, & they were unaware of it. As far as they’re aware, it’s not a feature. But it’s also worth noting that most the Seat staff, be it salesmen or service desk know very little about the EV side of the car, or its software. In fact, it was in for a software update, which they only were aware of as I mentioned I had read about it on these forums.