quality? Hmmmm.....I'd have to say I think plastic quality has IMPROVE if anything. Just take a standard klicky from vintage and compare with a new klicky. New klicky feels more solid and not as thin and flimsy. Also much less prone to loose arms/legs. Plastics now also less prone to yellowing.
I do notice on the newer design 4290 ship, however, standing rigging is made of cheaper thinner plastic that is brittle and not durable as its vintage predecesors.
And overall design of new playmobil is not comparable to vintage level of detail and aesthetics.
But as far as quality, for the most part, IMO, I think the plastic is actually better.
However, system x buildings, IMO, do seem a bit thinner and less solid than old steck pieces, which are built like rocks. Not to mention, they come apart much more easily than steck.
I also see many parts that were once metal (like anchors and bells and hoists) are now being replaced with plastic ones of the same mould.