The all-knowing romance character was quite common in early Harlequin romances.* This is the romance character who shows up and sneers at others while informing the lover, "I KNOW what's best for you. I KNOW you truly love me."
Unlike this same character in fantasy and sci-fi (and even there, it gets tiresome), the romance all-knowing character is a jerk, male or female.
And, as I mention on Votaries, even in fantasy and sci-fi, it is best if that character has depth and some uncertainty. For instance, Tolkien's mentors are limited in their knowledge, and they know they are limited. Even the kingly Aragorn gets frustrated at the breaking of the fellowship and blames himself for waffling over whether he should he go with Boromir, which he wishes to do (and has an obligation to do), or with Frodo & Sam, now that Gandalf has seemingly perished.
It is best in romance if this character is also limited.
So, Duke Avon in These Old Shades comes across as sarcastic and aloof and smarter than everyone else. And Leonie rather worships him. But he loses his cool when confronted by his ex, who points out that he has changed. He at first intended to use Leonie as a weapon. In the end, he wants to restore her to her position.
And Joan calls him out when he gets truly pompous. 
Back to romance! In Dangerous Convenience Store, the masterful yakuza-next-door, who wants to get out of the organization before he tells his lover all about his past, actually puts the relationship at risk with his aloof "I know best" attitude. I find the series quite impressive (so far) because the ordinary college student protagonist doesn't pretend that his semi-boyfriend's occupation might NOT be a problem. Love DOESN'T conquer everything. Being in a relationship with a gangster is NOT a good idea.
In addition, in Dangerous Convenience Store, the masterful yakuza-next-door doesn't feel masterful. Rather than inviting the audience to be awed by his masterfulness, the reader is encouraged to see him as trying to fix a situation he may not be able to fix--and he knows it. (He is rather like Jane Eyre's Rochester: he appears masterful but is a kind of Golden Retriever underneath.)
The well-rounded, limited character is always more appealing than the all-knowing one. After all, in One Punch Man, Saito carries his uncertainty with him.
*The character is making something of a come-back in romances these days--I will discuss why in a later post.
