It's a most excellent video but the curve he's showing should not be taken as the real slip angle curve. What it could be is one tire as measured by one manufacturer, to perhaps 10 degrees of slip. A different but very similar tire could have a very different curve, at least according to the data. Niels Heusinkveld talks about real tire data here, and shows just how different the curves can look. Yes, that's interesting but the data isn't conclusive. The slip angle curve changes with load and combined lateral and longitudinal slip. Peak grip can shift to a much higher slip angle and gentle drop off - even to the point of peak grip being with the tire going completely sideways. Overall grip would decrease, at first by a little and then by a lot, so the peak you get under certain conditions is not necessarily the maximum amount of grip you can get out of the tire. So you see, maybe your results here look strange because of the assumptions you make on how the curve should look? It could very well be that the results are spot on. Again, Niels talks about it here: Actually, you are losing grip. A few percent, so it's not huge, but still. Question then is, what would the data from a real car look like? Understeer being a bit slower but much easier to drive certainly makes perfect sense. If it's not punishing enough, then how punishing should it be? We don't know... Maybe it's exactly as it should be? Of course it could be wrong as well, but it's not exactly obvious that there is a problem here.