Agree with some of this but not all.....
My first "proper hunting break barrel" was a Mercury. A "wobbly, pin" one. And I learned that rifle inside out and we had many successful rabbiting and ratting forays. But when I first then looked inside a HW35 and then my FWB 127, it became apparent that internal finish / quality of engineering / solidity of build / materials were poor relations to the German rifles. I later also owned a Challenger (complete with daft sxope rail) and that wasn't really much better. And, yes, it did have a bolt, but it wasn't the mega solid one as used by Weihrauch and, as up above, some more "budget" rifles.
Firing cycle as standard, maybe the Mercury was a little nicer than a 35. But by the late 70s, many could perform a simple "spit and polish" fettle, which then transformed the 35's manners. And the triggers were far superior, aiding longer range consistently repeatable accuracy.
As you say, the arrival of the 77 was probably the final nail in the coffin. Webley did fight back with the Omega and Eclipse, but it was too late.
I have, however, had a couple of tries with the Superstar and find it a lovely rifle to shoot. Nice underlever catch, too.
And then we had the Venom inspired lovely Brum Longbow......