old glass hull v. new glass hull
I would say a whole lot more is known about fibreglass and the assorted other asspects of building boats now vs. 20 years ago.
In your question you ask "everything being equal". It''s never that easy. There are a host of tradeoffs when comparing even two new boats. On any boat you need to know is the hull damaged, in poor condition or suffering any of a multitide of diseases.
Newer boats can have problems just as well as old boats. They all need a carefull examination by a surveyor.
I have an older boat with an excetionally thick hull. It''s heavy! Some old boats have very thick hulls and it''s not that they are "better" it''s more like they didn''t always know how thick to make them so they were conservative. I would not mind if it were lighter but there are a lot of other things I find desirable for the price I paid.