I kinda think that the demographics are WAY to permeable. I had a 60hp panel van cannibalize my Family Sport segment, and building Pony Cars seems pointless because almost literally anything is a good Pony Car. Maybe some prerequisites/restricting criteria in addition to the percentage makeup would be good, f. ex.: All Family and Commuter type cars MUST have 4+ seats, all Delivery type vehicles MUST have a paneled rear, all L. Sport and Sport type vehicles MUST have a 2-door body (else: competitiveness automatically set to 0). Maybe desirability thresholds could be added, too, f.ex.: Weight over 900kg for L. Sport, length over 3,75m for City or passenger space under 2400m^3 for Family/Commuter reduces desirability (much like old body/rare fuel etc)
The main issue with the demographics right now is that there is not much in the way of proper competition in them and so you get cars that should not do well in certain demos doing so.
An example goes something like this
Fred wants a sport convertible, but there are no convertibles at all. Fred still needs a car and buys the closest he can find which would most likely still be something sporty. In that example a non-convertible would score in the convertible demo.
Going forward there will be better competition and this issue should go away
Yet still it looks funny when your big V8 SUV scores great as a fruinian premium city car 
Edit: but as a second thought, that’s quite realistic, considering what people use to move around the cities…
Yeah, I do think this is part of the issue. However, it happens all the time that even when you have a better car in a certain demo, it gets cannibalized by a car that does’t even make sense in that role - the 60hp panel van scored 120+ in the family sport demo, which just feels very, very wrong.
The demographics are screwed right now and there is no way for us to easily fix them. That is what the next big update is about for which we develop a car building AI that will generate new competitors with very few gaps, if any. 
Now that’s an encouraging thing to hear. Can’t wait to give it a shot once it’s out