In a somewhat idealised situation with huge torque from a large capacity turbo-diesel, the brakes are the only sensible way to control the speed as the idle torque is enough to break site speed limits of 5mph - on smaller capacity engine, a combination of throttle and brakes may be needed.
The issue here is always the spinning engine. You have to have some mechanism to get from always turning to barely turning in a gear ratio that is too high for the movement speed. In ICE cars, there are three ways of doing this.
- Manual clutch (ride the clutch, excess energy is dumped as heat in the clutch plates). The user has as fine a control as their foot will allow.
- Torque Converter auto (excess energy is dumped as heat in the transmission fluid cooler). Fine control is defined by the grabbiness of the brakes which will hold the car agains the transmission.
- Dual clutch. (Excess energy dumped as heat in the DCT). Control here is at the mercy of the computer that runs the DSG and modulates the clutch and the brakes. This (I am told) can be horrible. I confess, I have never driven one.
For DD - the beauty of EV is the basic problem changes totally. There is no spinning engine. The electric motor will deliver huge torque at minute RPM (as in 0 RPM). This means that the low speed control is as fine as the software that decides how the car will respond. It can be superb (as in the Polestar) or not quite so superb (as in the Fiat).
I should say though, my comparison of the Fiat is against the Polestar, which is the most precise low speed car I have ever driven. In comparison to my children's old manual Kia Picante, or the old XC90 TC auto, it's actually very good.