The thing that Zoro’s character misses from his peak in pre-skip is funny moments. Off the top of my head the last really funny moment with Zoro was the scene where they accidentally took Neptune hostage, he’s insulting Sanji, Brook is keeled over laughing, Nami’s cheerfully using it as an excuse for extortion and Usopp’s having a full blown panic attack.
After that you’ll still get great fighting moments, you’ll get good “Zoro takes this shit serious moments”, the general badass stuff, but the little sparks of humour (even if the humour is from him being deadpan/a moron/a dick), I can’t really recall. Just an over-reliance of the getting lost and hating Sanji gags.
It’s not the “he doesn’t smile” complaints, he smiles plenty. It’s the humour that’s been lost