Hi Bob. You’re right that the cars can feel quite jerky and it’s not possible to get them to roll when you lift off the throttle.
While you’re waiting for a fix from Scalextric or a third-party modification, there are a couple of things to look at:
1) adjust your driving style. I ran an ARC Air layout at a public event recently. It was a smallish track and we used the Scalextric Mini Coopers with strong traction magnets. There was certainly zero roll! Our racers were all ages - novices, home racers and serious club racers - including a European Championship podium finisher. Most people took to the challenge, although those used to racing with no magnets and lots of roll took the longest to adjust. It’s a case of keeping the power in, so you are rarerly off the throttle, avoiding the dynamic braking and keep it smooth.
2) remove the traction magnets. A lot of people race with the car’s traction magnets removed. Although the dynamic braking still functions, it has much less effect without the magnetic downforce. It makes the cars more like classic 1970s & 80s cars. With the modern chassis, removing the magnets means cutting one of the tabs that hold it in - so it’s not temporary (although they could be glued back). Running non-magnet means using the Scalextric borders and barriers because the cars will drift more, plus you’ll need to look at a few tuning techiques, like truing tyres. There are some excellent tips here: https://www.scalextric.com/uk-en/five-top-tuning-tip-for-christmas
When I started racing digital, the guy who invited us to his house set up different sets of six cars, some sets with magnets, some not, some low and sleek, some tall and top-heavy. It gave us very different car characteristics and different racing challenges, although the fundamental digital skills of overtaking and pit stop strategy stayed the same.
P.S. There is an alternative controller to use with ARC - the Slot.it SCP2 with Oxigen module. These retail for £140 each (although I have seen them for just over £100). I have not used these with ARC, so they may also have the automatic dynamic braking issue when used with the ARC Pro power base.