Crewmeal:
I was thumbing through a copy of Airport Timetables UK for one of the late 80's summers last weekend, and you're right, there were several YYZ services per week, not only by WD, but also Worldways, and Air Canada too at one stage. I remember being told even before then that Canada was a dying market as much of it was visiting friends and relatives over there, and literally they were dying out - that must to some extent be the reason for the collapse in the YYZ market from BHX, and I think it's mirrored at many other airports.
I also noted that there were, in the edition I was looking at, only one KLM and two BA AMS per day, one LH FRA, and generally very few high frequency services to Europe's main hubs.
I think the front end passenger nowadays uses the main alliances and rather than driving to LHR to get to heaven knows where, they use BHX, via FRA, AMS, CDG, BRU, ZRH, CPH, IST, DXB and EWR to get to where they need to. Those passengers haven't stopped doing it, they just do it differently.
As you said, unfortunately the arrival of the LoCo phenomenem has killed off some of the legacy carriers regional operations, and in my opinion is generally bad for the industry (where employees now have to work ever harder, for less) and the passenger that is stung by spurious charges for everything from plastic Bags and trolleys to car parking to pay for the fees that the airlines are no longer prepared to.