E36 and E39 cant be compared for 2 reasons.

The first has already been stated, a 3 Series and 5 Series are designed to do different things in different ways.

Secondly and more importantly in my opinion is that the E36 and E39 are from different generations of design even though their production overlapped slightly for a few years.

The E36 spawns from the E32 generation and up. And the E39 spawns from the E38.

This is btw how BMW release new designs and technology for those that dont know. New design philosophy and technology starts with the new 7 Series and then filters down through the forthcoming lower models.

So of course the E39 is a better built than an E36 because the whole way BMW designed and manufactured cars cars had moved on 10 years.

A fairer comparison would be an E34 vs an E36.