argue that the Romulans would design their ships with the specific goal of being better than their foreign counterparts. The Galaxy
project seems to have been a very public one, with all sorts of lowlife enjoying access to detailed information about the design. Backstage sources also suggest it to have been a lengthy project, dating back to the 2350s. The D'deridex
might have been designed with the sole goal of being better than the Galaxy
(even if by a crucial smidgen), with impeccable Romulan intelligence work establishing that the Federation wasn't planning on anything bigger or more powerful in the near future.
A more open society would just get entangled in a rat race. The standoffish Romulans could essentially keep their empire undefended for decades, skipping the construction of "intermediate" types while hiding behind the Potemkine facade of a thoroughly militarized star empire, so that they could pile up resources and unleash a superior design right when their foes had concluded their own supership construction work.
The Royal Navy sort of feared something like this happening for the entire duration of their dominance of the seas - which is why they refused to be the first to develop any really powerful or advanced ships, knowing that if they did so, some enemy or another would simply build a smaller number of even more powerful and advanced ships on knowledge stolen from Britain, and attain local dominance that way. Better to remain mediocre in terms of equipment, but absolute cream of the cream in terms of training.