Never had the pleasure of flying the Trident but was on the S1-11 during the corresponding period. I would not say that this was true on my fleet at all, most of the Captains I flew with in the early days were ex WWII and a real pleasure to fly with. As with any fleet or airline there were some who were less fun to be with than others but I can remember few if any that were "difficult". They had all transitioned to the 1-11 from the Viscount, Vanguard or Comet and were mostly excellent aviators.
However I did hear it said (on my fleet, at least), that those who needed two co-pilots to look after them went on the Trident whereas the more competent went on the 1-11. Again, I am sure that there were many exceptions to this rule - were it true - but it did make sense for the less able.