If you believe that Charles should not have been in that last fight, then you might as well say the same about Wesley being in the fight that led to his death.
And again, why was Charles called by his surname Gunn, in compare to the other characters?
I don't see any real proof that Charles was a better fighter than Riley . . . or if Riley was a better fighter. But Charles was more than just "street smart". He was a very intelligent man. I DO get tired of people referring to him as simply "street smart" and nothing else. Is that how most people from lower-class neighborhoods are regarded?
He was called Gunn probably just because his family used to call him that, and then his friends started to and so on... That happens often, even in real life. Weither it's nicknames, shorter first names ect... 😛 Think of Giles... his first name was Rupert, but only Ethan & Jenny ever called him Rupert more than once.
As for Gunn being a better fighter than Riley, who knows! He did kill a LOT of vampires all by himself in 'Not Fade Away'. I don't think Riley could have done that. But to be honest, characters strength in both shows have always been really variable...