"Only" means it was the only ship mentioned, so that's all we have to go on.
Yeah, I know - sorry about deliberately interpreting it the other way. I wanted to emphasize that Pike is not one of those special cases known to have only commanded one starship in his career, or started out big, or something. Unlike, say, Picard, who made it explicit that the sizable Stargazer
was his first starship command.
As for fresh vs. seasoned, I saw Pike's fatigue as something he'd be encountering for the very first time, but would soon overcome, achieving Kirk-like greatness despite mounting Redshirt casualties. Speeding back home after losing a few men in a landing party incident is perhaps valid behavior for a CO, but when contrasted with Kirk's habits it looks timid and insecure.