its obvious that different types, brands and models of tyres offer different amounts of grip. No one's arguing that. But as per my example of the exact same tyre, you get the more grip from the wider widths. Thats removing all those variable you keep trying to squeeze in.

I'm not saying he shouldn't try to choose the tyre that offers the best trade off between grip and life for his purpose, just that he should also use the widest one he can fit because that will offfer better grip. If your argument was true, we could all save alot of money and buy the narrowest of the good tyres as it offers exactly the same amount of grip as the wider ones. Its nonsense.

you're so bogged down in theory you're confusing yourself.

Ever noticed how F1 cars don't use skinny tyres? they would if they produced the same grip, because they'd be lighter and offer less drag, bother of which would dramticaly increase performance. But the fact is they can't get the same grip from a narrow tyre.

Ever notice how top fuel and other big bhp drag cars don't use skinny rear tyres? They would if they could get the same grip beacue narrower tyres would also give less aero drag, making them faster in the top end. And because wheels and tyres are flywheels - you waste energy turning heavier ones. But they don't because they need the big tyres to get the grip they need.

Which is one of the reasons why your example of the low powered car went faster with the stockies rather than the large diametre tyres. smaller, presumably lighter stock wheels and tyres waster less energy that can then be used to accellerate the car. They'd also have less rolling resistance, And also lower the gearing, meaning better accelleration. And yet another being because it simply didn't need the extra grip of the bigger tyres.