>It's a lot harder to fake incompetence and failure and besides why would you?
Whether Gordievsky was a triple agent or not, it's clear that the KGB desperately needed a conduit to convey useful (true) information to the West in a form that Western intelligence agencies would find credible. Western intelligence (particularly the UK) also desperately needed an asset who could produce that sort of intelligence. Gordievsky just happened to be a perfect conduit for this communication, and may have helped avert a truly stupid nuclear war.
If you assume this was an "op" then it would have to end somehow. Ideally it would end in a way that left Gordievsky alive and in the West, where he could continue to deliver his message to politicians. In order to keep Gordievsky's past information credible, he would either need to (1) be caught and tried/imprisoned, (2) defect. But I would imagine that the best case for his credibility would be some amazing combination of (1) and (2), especially a situation that would force the West to commit resources to a heroic escape that took him right out from under the KGB's nose in Moscow. This would make his handlers look brilliant, and it would make Gordievsky the kind of hero that politicians would take seriously. It would also be politically almost impossible for anyone in US/UK intelligence to ever (publicly) voice skepticism about Gordievsky.
Gordievsky's escape from Russia also seems extremely bizarre. Remember this is a man who has miraculously survived chemical interrogation, is liable to be shot at any moment, but has somehow slipped his KGB tail and traveled halfway across Russia to a border town. Whatever doubts the KGB had before, he is now a dead man if they catch him. Yet instead of hiding in the woods waiting for his rescue, he heads into town, gets drunk, falls asleep in a restaurant and nearly misses the appointment to escape to the West? I guess people behave strangely under stress, but there's strange and there's "death wish." Perfectly reasonable, though, if the whole thing was fake.
Finally there's the fact that Gordievsky's arrest story was almost immediately verified by Vitaly Yurchenko, whose "defection" is utterly bizarre. Yurchenko just happened to be an expert in "special drugs" who defected right after Gordievsky escaped, basically for the sole purpose of solidifying Gordievsky's story and drawing attention away from Aldrich Ames. Then, literally weeks after delivering his confirmation to US intelligence, Yurchenko walks out of a Washington, DC restaurant and heads straight back to the USSR where he is awarded the Order of the Red Star for "a successful infiltration operation."