What exactly do you mean proper “dark” themes? Being able to swap to coding in light test on a dark or dark text on a light background goes back to at least windows 3.11.
I would assume 'proper' means 'adequate in terms of function and aesthetics'. maybe something like 'themes that don't eschew real usefulness'.
those themes did exist before solarized, but they were not the norm in many circles (mine included), as many authors did sacrifice function for the look&feel.
solarized demonstrated how to apply colour theory/science to the landscape.
I would add that it has been not just the theme that serves as an example, also the _how to make_ a theme following those principles.
Fair enough, I have the opposite experience where most people using dark UI’s where doing so for utility reasons not aesthetics. Outside of a brief fad of Matrix themed terminals which quickly died out.
Solarized dark theme to me looks just like several other similar themes that predate it ex: https://superuser.com/questions/156979/how-to-i-use-textmate...
But I assume you have something specific in mind here?