Fair but who says she’s doesn’t? I haven’t seen her show but she’s certainly capable.
It’s something I often pay attention to - some artists will perform some of the parts live and even that is annoying. Full fake is just abhorrent.
But nobody should assume a performer is lip syncing without evidence. Or if he’s referring to the fact that some element of music itself is a produced track or effect that isn’t reproduced in the live show? I think that’s pretty common in pop music but even Paul McCartney does that.
You know who lip syncs during some of his shows? Garth Brooks. It was pretty obvious to me (my wife is a fan, I’ve been to shows) - but the audience seemed to not notice or not care.