Notice Nornagest didn't criticize all the other character-building repeated elements/motif/themes which range from humor to philosophical to tragic, like the watch, which suggests to me that he simply doesn't like the jokes about height, not that he is making any real point about the general desirability or functionality of these mixed genres.

Hey, that was your example, not mine. I was actually thinking of some of the silliness in Seras Victoria's scenes in Hellsing when I wrote my original comment, although that particular style of comic relief is common in the genre and FMA isn't terribly shy about using it. The other repeated motifs don't bother me because they aren't incongruent with the local tone of the series.

Comic relief also isn't the only place this sort of thing shows up, although it's probably the most common: a lot of anime takes a similar approach to erotic fanservice, for example. Although now that I think about it, that version does happen fairly often in Western media...