Hello, thanks for your message !
Sorry I missed thoses electric hovercrafts :)
About slowing down I'm really not fond of it. I feel the plating are balanced as is being kinda expensive and vehicles having very limited grids (at least from the default grids I add).
From my playthrough it really helped scaling survivability in harder evolution of the car and the tank and I feel that having a slow down (even if it somewhat makes sense) would nerf the usefullness too much.