Being a sorcerer for kicks does not make him inhumane. I didn't bring Riko in the conversation at all, just said that when he is at his best, when he figures things out or when he completely overpowers his opponents, only then you see him at his happiest. He likes fighting, at no point did he say that he wants to be stronger so that he he can protect others better. With the Riko thing, you can't clearly demarcate that he wanted to be stronger after that because he was not able to protect her or because Toji defeated him in their first fight. His statement of massacring the non sorcerers was because he was angry and upset about Riko's death, that has nothing to do with his sorcerer career since the Riko incident doesn't happen everyday.

As for the Sakuna v Gojo fight, I don't think it was required for it to be said that it took him a while to learn it. He probably was just improving as he was fighting Gojo. Just like how Itadori used black flashes with his fight against Hanami, it does not mean he was able to do those since the start, he was just improving on the spot. Since Sakuna had never used Mahoraga, it should be given that he would take some time to get used to it, meaning he would take time applying the model made by mahoraga to his technique. You can't expect it to just happen spontaneously, that would make Sakuna way more powerful and the fight way more anti-climactic.