There are LOT of main characters, even in standard shounen-fare who win most of their fights convincingly and few chapters further in the story you're still convinced that it was a deserved win. Kyo from Samurai Deeper Kyo, Himura Kenshin, and the Black Cat, for example. Ichigo doesn't fall into that category, but like I said, I'll give him time. His "random power level" also gives Kubo a perfect rationale for writing Ichigo like that.
And oh, you honestly didn't expect Goku to beat the pulp out of Vegeta, discounting a Vegeta power-up? That was the entire purpose of his training. Never read Inu Yasha nor those one with Butch and Hiro, so don't know about that.