This is just an impression, because I don’t follow entertainment/culture the way I used to. But …

When I was growing up, it seemed like all the best pop culture was British. I mean the great totems like the Beatles and Monty Python. Nowadays not so much. Still a lot of cultural prestige, and still a lot of very good British actors, directors and musicians, but no super-heavyweights. Any of them could be replaced and the pop culture of two continents wouldn’t shake.

I would say this has been the case since the 1980s, with the exception of US commercial comics. In that field we have a couple of figures whose presence has been game changing: Alan Moore and Neil Gaiman.
But the Spice Girls, Guy Ritchie … ? Britain’s record for generating pop phenomena seems to be getting thinner.  Fads they can still do, and as noted they keep turning out tons of accomplished professionals. But not phenomena.
Maybe that’s no big loss, depending on how you feel about phenomena. At any rate, a change seems to have taken place.