I think most mainstream volume manufacturers build quality has declined. The possible exceptions to this are Royal Enfield and some of the Chinese brands.

But build quality has different interpretations. Does it equate to reliability? I don't believe that is necessarily the case.

A bike might be exquisitely made with beautiful components and delectable materials all finished with lustrous paintwork but that doesn't guarantee it won't breakdown or suffer dreadful corrosion.

At the other end of the spectrum something that looks rubbish might prove to have bullet proof reliability.