my mate has had and old shape Merc C-Class and a current shape one
my ex gf's dad had an old shape E-Class and i've been in a current one too
and my parents have both an old and current shape S-Class on the drive
all all accounts the newer cars are better build
Mk5 wise a lot of the commentators reported the Mk5 wasn't as well built as the Mk4. when i was choosing a car that's what swung me to the Audi. the 8P is, to my eyes, better built.
BUT if you asked me to pick between a Mk6 and an 8P the Mk6 would win hands down. soooo i don't think it's as simple as everything's getting worse as time passes