I always found it sweet how Damon took care of Bonnie in the books, and I thought it funny how Bonnie admired Damon; but it is a kind of father-daughter-relation for me (or - like you said - big brother and little sister is also fitting). I stopped reading after "Midnight" so that I don't know what happened after that, but it was only about gratefulness and protection from Damon's side until then, while Bonnie had a thing for almost every boy and was childishly romantic in everything. I never thought of any real love between the two of them until I heard about Bamon fans, because there was never any passion between Damon and Bonnie and there was nothing to implicate Bonnie as a serious option for Damon in the books, and I still see Bonnie as Damon's little redbird and nothing else while Elena is his soul's eternal mate, twin flame etc., and Delena have really everything between them. So, I can't give you an answer to your question, but I agree with you. No love can even get close to standing up to the Delena love story, but I never came across anything while reading the books that makes Bamon worth discussing it at all.