I took history of christianity last semester, and I read a lot of translations of latin works (the translations dated from the era of public domain so that may be part of the reason...) and I'm currently reading a translation of "meditations" by marcus aurelius from 1800 and the sentence structures are terribly, excessively complex. Do I just write like an idiot, or did people legitimately write differently back then, and if so what changed?
It's not. It just seems that way.
You are generally reading literary and theological texts, that are written in a more educated style; it would be like reading dense academic texts.
You are reading 18th and 19th century translations, which have a different style of English, and are trying to replicate Latin sentence structures, so it reads poorly (well, with difficulty) in English.
It's not Latin in particular that causes you this problem.