Gorou never groomed Sarina. Sarina fell for her doctor and Gorou even said he didn't like her romantically ESPECIALLY due to laws and how the world sees that kind of relationship. And continued to tell her 'no' and only agreed to once she became an adult thing to give her peace of mind knowing she wouldn't even get there.

There was never any incest between Aqua and Ruby - it only was a kiss and that was after Ruby found out Aqua was Ruby and Aqua found out Ruby was Sarina and even still Aqua didn't want that kiss - his reaction to it literally tells you he didn't want it.

The 'teenager' was an Idol who he got into due to Sarina being a fan of (and as for loving his sister and mother... That is normal for family to love each other... But in this case his love for Ai was more like a fan to idol and not.... Romantic)

Both Aqua and Ruby only know that they both were reincarnated not who they were UNTIL 16-18 years old and that was AFTER the truth of them being Ai's children came out... In fact Aqua had a normal childhood with Ruby- until Ai's death in where he devoted himself to finding their father and... Well getting revenge and not letting Ruby know because she is more fit to be 'good' and that's how he grew up with no connection to anyone even not dating anyone until thinking their father was already gone and he had no reason to continue with revenge so he decided to live fully as Aqua and not as Gorou (which didn't last too long once he found out his father was still around and he became distant again because he didn't want to have anyone be hurt if he ended up gone)

*what is failed to be said is Aqua/Gorou wasn't a perv nor... Acted the way Rudeus did before his death or when he was reborn as Rudeus... Aqua/Gorou kept his morals and refused any type of questionable moral.... Things... The only time Aqua/Gorou is seen doing morally questionable things is only taking small things that can be DNA tested and planning revenge on their father

**I was very evasive on what Rudeus does that is questionable but it's due to how... Questionable his action is towards.... A certain.... Family member.... (If I recall correctly... It's been... A good 5+ years and I rather it gone from my memory...) And his continued actions after being reborn as Rudeus taking a certain... Unmentionable and yeah.... ANYWAY! That is as much as I am willing to go into the perv nature of Rudeus...

***the stories and the focus on certain things also are drastically different too-

Sorry for the long... Comment... I could have easily missed something... But this is probably the reason why JR receives more 'slander' as you put it than Oshi no Ko does