I get really surprised when people act as if Daikichi was a groomer. I might be misunderstanding the paralells that people keep pulling between Usagi Drop and ex. Tale of Genji, but I never once got the feeling that Daikichi had any intention of thinking of Rin as something else but his daughter until he was pressured into doing so by Rin and Rin's mother.

I always find it so sad from his perspective, especially when Rin corners him and (if I remember correctly) tells him she never viewed him as her father/he shouldn't view her as his daughter.
It was his whole life up til that moment, and he responds with being hurt and angry by this, since he obviously viewed her as a daughter, wheras Rin saw Daikichi as Daikichi.

Ugh, I just feel bad for him. Because eventhough the ending says: Yeah, he decided that it was okay to get together. I can't imagine him not agonizing over the ways things became.

Or maybe I'm just wishing this ¯\(°_o)/¯.