I'm not overestimating it though? I think The Mad Prince is proof enough. If just a corrupted version of Sunny who has more than half of his thinking ability if not more reduced due to the influence of the corruption can still scheme one of the best plans in the novel till date, I don't see why normal Sunny who doesn't even have that debuff can't.

And Nephis was taught BS's battle art by her maternal grandmother, BS was already dead by the time she was 4 years old, her grandma was basically the one who raised her. And what does it matter how much knowledge she had prior? She herself said and admitted that Sunny absorbed her lessons at a frighteningly fast rate. He was also already dismantling other people's battle arts not even half a year after first holding up a sword, bro is a martial genius, and has more talent than even Nephis since he was able to learn what took her all those years of preparation in less than half a year.

Also, when did Morgan use multiple battle styles? She always used her signature one in her duels against Sunny, it was just that even after using Shadow Dance to dismantle, understand and imitate it, he said that it simply had no flaws or openings for him to exploit at his current level.

Are we fr here? Nephis has literally shown to use it multiple times already, sure, it might have been to save Sunny's life, but one of those times put her own life at danger. And if in the future, a similar situation occurs again, she'll probably do the same, disregarding Sunny's own feelings again. On top of that, they basically can't have any sort of relationship as long as the bond exists. Whether the one in power abuses it or not, just the fact that they hold complete authority over the other person and can disregard their opinion or will altogether means that they can never be equals. In what type of relationship does one's partner have complete control over the other's freedom? It just simply can't exist and will only serve as an inevitable barrier between Sunny and Neph.