I try to make a distinction between "admirable" and "likable". There is always an appeal to competent characters, the badass winners, and those who get away with things. Even the most selfish characters are appealing that way as long as they are competent. Often we think these characters are "cool", but we don't necessarily "love" them. Maybe those would have been the better distinctions.

Roger is an appealing character because he is competent. We think he is cool, no matter how selfish he is. But we don't really "love" Roger the way we love Whitebeard. There's a different quality to the appeal.

The issue is that Oda tries to make people "love" Oden. Look at how the scabbards cry thinking about him, and how Yamato says Oden's life brought her to tears. That's not admiration of a cool persona but something beyond that, which selfish competent characters normally only achieve by being less selfish.