I'm not going to argue with anyone's view what is great Brahms and what is not, but I have a feeling stuff like that might be representing rather contradictory (and maybe opportunist) sides of his character. Brahms admired Wagner, but mistreated Wagner's followers. Also, considering Brahms ended up criticizing Beethoven (in terms of style of vertical harmony)
You still have not understood that your continous cherry picking leads you astray yourself. You pick one small critical remark by Brahms and ignore the overwhelming dominating influence by Beethoven, maybe because the latter is taken for granted anyway, so you overstress 1% vs. 99%.
It's uncontroversial that early Brahms and especially the serenades are strongly classicist pieces, it's what he dared to write when he didn't dare writing real symphonies. It's also not about personal admiration, more like demonstrating that one knows the craft and the classics. The first movement of op.11 almost quotes (in fact many people take it as a quote) the finale of Haydn's 104, the 5th movement is roughly a combination of the scherzi from Beethoven's septet and 2nd symphony and the menuet sounds like from Schubert's octet to me.
Regardless of specific allusions it's obvious that Brahms was treading carefully and mostly staying within a very conservative classical framework. I cannot "prove" (not even sure how one could do this) that mvmts 2+3 are more original and "Brahmsian" but it is fairly obvious to me if one is familiar with his style, it's the mood, the sound, like the first scherzo is subdued and lively at the same time etc. It's not found by cherrypicking, though, one needs a more holistic approach.
