...I finished the buildings AND wonders in less than 48 hours, across two days where I didn't spend much time on it.
I legit have no clue why the process for these is so much faster.
I will need to do a second pass on all units/buildings/wonders once I get the tech tree done. (Which is what I am doing next. Tech tree, governments, can be done in either order but tech trees first makes more sense to me now.)
And then a third pass to make each have a unique civilopedia entry so that it's actually possible to know what each unit and building actually does without my creator knowledge.
But the initial stage is there.
I'm definitely making a lot of progress there.