Ladybug (or ladybird over here) joke is just funny. I’m sure there are millions of male ladybugs (or ladybirds, which is worse, considering the British slang use of bird to describe an attractive female) that get annoyed because they get mistaken for automatically being female because of the name.
As for Heimlich's manoeuvres (haha) at the end, I never took that as a fat joke, since he spends the whole movie waiting to have wings and then, when they come, they’re inadequate for even a slim Jim caterpillar. But just the fact he has them makes them special enough for him: it’s not about how big or small he is, or how big or small his wings are: he is overjoyed in the moment and we should feel the joy in his joy, as the rest of the cast do by helping him achieve liftoff. It’s not that he's large, but that his wings are small, though it doesn’t matter since at least he *has* the wings he’s been waiting for.
Newman's score is more of the "pure Americana" that infused the early Pixar films, because that's the background the filmmakers knew, and/or the long-lost feel of nostalgia that they wanted to recapture. No, maybe A Bug's Life's score isn’t as epic as it might be, but then it *is* an epic of *miniature* proportions, so the music can’t be *too* large scale, and is more about describing the characters and situations rather than giving the movie scale, the widescreen framing and full orchestra do that already.
At the end of the day, and no pun intended, A Bug's Life is a "small" movie, and I think the score reflects this pretty well, since it’s not a large scale action picture (even on a bug's scale) but more of an adventure of self-discovery, whereas Antz — which arguably is the better, smarter, funnier, and less "dated" film — with its military aspects, definitely is something of a massive action picture, and has the modern action score to go with it.
Bugs remains a slightly lesser Pixar output, but it was massive and hugely beloved when it came out, even moreso than Antz that year. To overuse the obvious description it is a small but perfectly formed little movie, in pretty much all ways. I don’t revisit it as much as I have Antz, or other Pixar films, but I have fond memories of it, and of it's not a massive film with a massive score, it remains a safe, almost cosy movie that’s a nice throwback, which is exactly how I think it was intended.