Your claim is something different.
You're claiming that _relative to newer buildings_, yours has lost value.
The parent poster is claiming that _relative to the same building in the past_, prices go down in japan and up elsewhere.
Would the apartment you live in now have cost more or less 5 or 10 years ago? That's really the thing the parent poster is talking about, and other newer constructions are unrelated to that point.
A small, new apartment next to the old, big apartment I live in is much more expensive than mine. And mine was considered high end when it was built.