I think Lucy was overall just too good to be true. Also Soviets thought so initially
Information was accurate, timely, and covered all areas interesting to Soviets in their war against Germany.
OK - i guess it is possible that there were high ranking, extremely well connected spies that had ability to use Germanys own command and control system to forward the information to Switzerland - the thought of group (or even just one person) being able to gather such critically important information, and successfully run the operation undetected for years tickles the curiosity of everyone interested about these kind of aspects of war...
Nowdays i myself believe, like many others, that Lucy spy ring being SIS operation (thus information coming from code-breaking) is the most propable explanation.
Regards, Mark V