I know exactly what you mean. But watching the scene where the US and UK security chiefs have the meeting, it is quite clear that the US had already worked out that Pym was a spy and the British were made to look a bit silly with their "but he's one of us" attitude.
One of Le Carre's failings, IMHO, is his inability to portray "ordinary" people.
By that I mean anybody who does not fall into the English, upper-middle class, privately educated, moneyed bracket. It is very evident in his novels. And it is very evident in this TV adapation. The "working class" are almost cartoons.
The two ladies who have taken care of the body of Rick Pym, come across as cackling old crones from a poor Dickens adaptation.
It infuriates me sometimes, but the lad can spin a pretty good yarn !
I agree with you on Carre's writing of "ordinary people". A common failing of Oxbridge type writers, Colin Dexter is equally as bad.
As for his being "anti-American? Who with any taste isn't?
Marlon, Claudia and Dimby the cats 1989-2005, 2007 and 2010.
Showing Pym in Palm Springs instead of say the Smithsonian museum was used to show how Pym's ego had become so greedy and crass.
The meeting with the American was very much about snotty Oxbridge types looking down their noses at the mediocre cowboys.
THe end bit of the scene when Grant(?) confronts Jack one to one was very reminiscent of Columbo's 'just one more thing.'