Intelligence services are once again coming under correctly-directed fire
Not quite. They should come under fire that they had all the data needed and failed to connect the dots.
The biggest problem of intelligence today is not the lack of information, it is the information flood. The final links in the chain - the humans that are supposed to evaluate the processed information and make decisions are overwhelmed.
Banning or backdooring encryption will not help this one in the slightest. In fact, just the opposite. If they cannot handle the flood today, how the f*** are they going to handle the deluge in that case?