Excellent point. During the Cold War, the GRU often proved to be a more formidable adversary than the KGB, and it presumably remains so today. After the FSB botched the job of subverting Ukraine’s leadership so as to make the Russian invasion a walkover, the GRU was put in charge. It is not clear if they are more effective though.
The head of MI5 in the 50s and 60s was a GRU mole.