Ugh I know Leighton really does phone it in most of the time now. But even so, when she's given good stuff it still works.
But they've transformed Blair. She's a different person from season 1 and even 2 - and not just because of romances, but just in her pragmatism and how she was so good at playing coy or powerful or manipulative. Now she often just comes off as a hysterical loon at best.
Though when they were writing her and Dan with a screwball comedy feel I felt like that worked out rather well for both Penn and Leight.
I don't think Blake phone's it in because she has so much energy all the time, but there's only so much you can do with one note lines.