I don't think Le Carré was trying to write high art either, but I think they were interested in different things. Fleming wanted a fast-paced popular thriller, while Le Carré wanted a realistic depiction of spycraft.
Le Carré does provide a much more realistic depiction of tradecraft than Ian Fleming, of course, who is to tradecraft what the 60s Batman TV show is to realistic detective fiction.
I would not say that the point of le Carré is to realistically depict tradecraft. He's not a realism antidote to Ian Fleming. There's not really all that much tradecraft in a Smiley novel; they're much more about human relationships, and about the moral bankruptcy of the Cold War enterprise.
Le Carré is much closer to literary fiction than Fleming, who is a genre hack. Not so close as to be tedious; the books are all fun to read. I'd push back on the idea that le Carré wasn't aiming for art, though.
(If tradecraft is what you're after, by the way, what you really want is Hoffman's "Billion Dollar Spy".)
