There is also some confusion whether the F/O was PF on both sectors or not. Las Palmas is generally a more benign airport then Bristol in the winter; confirmed by the weather. If the F/O was on a series of refresher line training there is no problem maximising PF duties, If his only sector at the end of a long day was into BRS, that could be challenging.
There was no comment about why the a/c ended up requiring a G/A, other than it drifted off and became high.
However, to understand better root causes, it would require answers to A37575's questions about company philosophy and use of automatics; otherwise we can surmise, going round in circles, from an incorrect starting point. This topic, about automatic dependency, has been debated from all points of the compass and from every angle on many occasions here.