Personal I think they had it hacked all along. The FBI just wanted to make it appear they could not get in while they ran down all the leads in the intel.
An interesting scenario. Maybe also Apple’s public protestations were also part of the public ruse you posit, and they actually did help to hack the phone, but worked a deal with the FBI to go with this cover story so that they would display a public face of “customer concern”.
We’ll probably never know the answer to that. At least not for 50 years or so when the files may be declassified and available under FOIA.