Capet is only the personnal nickname of Hugues Capet (remember in his time almost everyone had a personnal nickname), no other individual ever used it in the dynasty before it was used at the revolution ... to ridicule the king during his trial. In the mind of the french people, heraldry and the particle system were strongly (wrongfully though) associated with the idea of nobility and the taking down of both was systematic. In the end, it's a exactly like renaming the Hauteville dynasty to "Bras-de-fer" or "Guiscard" : if some historian would decide to do that in the XVIIth or XVIIIth century, that doesn't make it any historical, just like the Byzantine Empire.
Philippe Capet, Sancho Jimena or Robèrt Bosonid are individual names that would never exist in any context (not even modern academic papers since they are incorrect in grammar or form) and since there's no way to distinguish the name of the dynasty from the name the individuals use ingame we're stuck with choosing one or the other. I thought people were against any kind of modern apocryphal name like Byzantine Empire but if the majority of players want them it's still possible go the other way, but careful what you wish for : there are hundreds of them and since first names are very repetitive there will be many identical dynastic names like Rodolphians or Willelmids.
As for the counts of Toulouse and Provence having identical arms : they used the bosonid cross of Provence as their emblem and had no other one. So did the cadet branches of all the families having a claim to Provence (counts of Forcalquier, viscounts of Marseille, the lords of Baux and Monteil). Those are the arms of the Marquisate of Provence which was at the center of the dynastic conflicts in Provence in the XIth and XIIth centuries. It's also no coincidence that the city of Pisa chose a very close design as it was the capital of the Marquisate of Tuscany (before the game timeframe), ruled by the same dynasty.
