Last Grid sold poorly through heavily publicised lack of content and average reviews, Grid Autosport launched on the previous gen consoles at a time where the Xbox One and PS4 had already established and Grid 1 and 2 sold and reviewed well.
A game that can be accessible will sell better than an outright hard sim. Grid will still sell better than ACC, because ACC has extremely limited appeal regardless of the views of Grid.
It has to strike a balance in the same way the F1 games do. Look at thenlikes of Gran Turismo, Forza Motorsport, F1, clearly the best selling racing games across the genre because they strike that perfect balance people crave. I'm not saying it shouldn't be a sim, but it has to balance all of the elements so that it appeals to the whole core BTCC fanbase, not just 10% of it, first and foremost.
Its been too long since the last official BTCC game for someone to completely miss the opportunity now to establish a really solid platform. Get good sales, get a good reputation, get some cash in and start building deeper foundations from there.