My recollections are that the 1st seasons Wardairs were all direct to YYZ. There was never any operational difficulties in getting direct with a full load. On departure the performance of a four engined a/c is good, but the 747 couldnt land on 14, causing 1 to divert in that 1st summer. Thereafter they went via BHX for one or both of the following reasons. Firstly, they didnt have enough a/c, or wished to do more from BHX, so decided to combine. Secondly, they quickly realised that LBA couldnt cope with a full 747.... the new terminal being totally and utterly inadequate.
The latter is the most likely reason as Wardair were sticklers for their quality service.... I remember they offered full china service with real cutlery!