The spawn non-romanced version is done better than when he's in a relationship, but I don't like his lines about inspiring hope and saying he's fine not drinking blood. Sounds too heroic and like he's becoming a Wyll wannabe. It would have been more in character if he said that he was taking some mercenary jobs for fun, to kill some people and to be able to drink blood of those no one would miss.
To me him accepting the fact he can't walk in the sun is him embracing his vampiric side and the restrictions that come with it, his inner darkness and integrating his shadow self. He feels fine with who he is but if he can find ways to get rid of the inconveniences that come with his condition then he'll take them, because he still wants to empower himself and live a good life. Cazador hated being a vampire and all the drawbacks he had to deal with, which can be witnessed if his mind is read when Astarion is not present during the encounter. Him becoming a vampire was his choice so I think he just means being ordered around and having to do others' bidding as something he wants to leave in the past because now he has the freedom to forge a new future for himself. It takes him a while to get out of the slave mindset, even if he's physically free from Cazador.
The life in the Underdark is brutal and the types he has to deal with were not nice people even during their mortal lives (he says folks like Sebastian were in the minority). He doesn't have any extra powers as he does after ascension so a violent display from time to time makes sense. The majority of them are still ravenous and only strength is something they would respect. Right after abandoning the ritual he feels hopeful that he can live a different way but when he's in the Underdark he gets a hit of reality. Being idealistic doesn't work in that environment.
He is selfish but he also likes having power over other people. It could be his way of experiencing that thrill even without ascending.
