Channel 4 has the best reality shows in the world for housing and architecture, featuring the irreplaceable Kevin McCloud (Grand Designs, RIBA House of the Year, etc.), Secret Millionaire for the philanthropic human story. BBC has the best gardening programmes, with the incomparable Monty Don (Gardners World, various travel gardening shows, and the RHS Chelsea flower show). The best nature programmes by-far with David Attenborough. The quality of cinematography, music and narration has no equal for these shows (when taking into account the scale and variety of shows available). And the BBC has the best sports coverage for a number of sports.
I’m not British, so my opinion is not biased in this way. I would say on the average US TV is worse for any kind of show like the above. You can take any of the shows Gordon Ramsay has done, for example and his British series are better than his US series. Of particular note is the annoying American TV editing, where they viewer and their time is treated with much disrespect. Way too many ad breaks, repetitiveness, dumbing down the audience and generally just too commercial.
Where US TV shines, IMO, is in the genre of great fictional TV shows. Pick a decade! Pick a genre! TNG, Quantum Leap, etc. etc. And film, of course. No example necessary.
British TV has also created some fine mystery series such as Miss Marple. And some fine films here and there, over the years. And, of course, a vast body of comedy TV series.
Blanket statements ignore the bigger picture, and I disagree with yours. Some British TV is not just great, but better than great.