G2.5P might've updated, but that's not the model I noticed a difference. o3 seemed noticeably dumber in isolation, not just compared to G2.5P.

But yes, perhaps the answer is that about a week ago I started asking subconsciously harder questions, and G2.5P handled them better because it had just been improved, while o3 had not so it seemed worse. Or perhaps G2.5P has always had more capacity than o3, and I wasn't asking hard enough questions to notice a difference before.