Without any artificial boost, the control surfaces could only be moved as far as the physical strength of the pilots would allow against the aerodynamic forces. About 50% of the full range assisted movement seems reasonable.
It would be interesting to know what the problem with the autopilot was and the process for disabling it when it was inoperative. Just a circuit breaker pulled, a fuse removed from a panel, or switched off with a placard placed over it.
If the autopilot was capable of operating the ailerons independently of the manual flight control cables, then this aircraft should never have been allowed to fly. With the auto pilot inoperative, the cable presents a single point failure mode where maintenance of normal flight becomes impossible.
A bit like taking off in a modern jet with only one generator operative and the other generator and APU flagged inoperative. It shouldn't ever happen, but it does.
One question to consider is whether when the cable broke, did the controls lock in position because the broken ends of the cable jammed and snagged preventing movement? That would certainly give the impression that the autopilot had somehow engaged and was fighting the crew for control. Under the circumstances it is probably reasonable to first assume that the autopilot has engaged somehow. Something as vital and simple as a mechanical control cable breaking would probably not be the first item to spring to mind, especially in what was a complex aircraft for those times.
So perhaps the root cause was that the aircraft was despatched with an inoperative autopilot, removing the only possibility of maintaining control in event of a mechanical failure of the flying control cables.