... but nothing's perfect, not even live music; it has imperfect venues to be played in.
We were discussing complementary transistors: PNP and NPN devices. They too are not perfect. Each alone has its own quirks but they are different. And that's a problem when we try and divide the top half of the sine wave using an NPN and the bottom half using a PNP as we do in a full complementary circuit. Were they identical it shouldn't be a problem. But they are not and try as we might, as designers, to match their characteristics we can only get close, not perfect.
To our rescue comes things like negative feedback - which some designers use while others eschew. No, designing circuits is always a challenge involving compromise, careful listening to the results of fixing one thing while breaking another. It's just the nature of what we do.
On a personal note I like and use complementary symmetrical devices for output stages, and have for years. They are the best of the compromises we have.
And that's important, knowing which are the best, which to stay away from. And perhaps most important, knowing what to listen for when designs are being evaluated.