Isn't talking about, and exploring things that you're not an expert in, good, rather than bad, as that's how you learn new things?
Potentially, but that's not what "sophomoric" means. It's roughly the intersection of overconfident and immature.
If there's a trope about people new to a particular field being overconfident in what they know, maybe it's just human nature rather than a fatal character flaw, or sign of immaturity.
(i.e. since you'll likely have the same sense of overconfidence the next time you try something new, or work towards mastering a particular skill rather than that overconfidence only ever coming up once or twice in your entire life)
It isn't really. Novice, for example, doesn't have negative connotations. The other thing sophomores have going for them is that they're typically teenagers or barely not, and an adult not having grown up generally does have negative connotations.