Why is Moby Dick famous and not The Sea Wolf when the Sea Wolf is a better nautical novel by every metric? It's "deeper", the stakes are higher, the characters are more interesting
Moby-Dick is a philosophical novel. It uses the nautical novel format as an excuse to talk about philosophy, just like Pierre uses the sentimental novel format.
Moby Dick has great prose and is funny. Is Larsen more compelling than Ahab? I don't necessarily think so, but it's apples to oranges, Ahab is a classical tragic hero overcome by anger that makes him violate the natural order (hubris), and he talks in Shakespearean ways. Larsen is not a tragic hero, he's an unsentimental but introspective villain