Currently I'm brushing up on Spanish in the same way and absorbing (for instance) the subjunctive painlessly.
I think most people still underestimate how easily an adult can learn a language.
"Paul Nation in a 2014 article estimates that to acquire a vocabulary of about 5000 words a student needs read about 2 million words."
If you absorb about 3000 words a day, after less than a year you'll have read 1 million words. With a vocabulary of 2500 words you can do quite a lot. For me, in Latin, that's about 40 minutes of reading (I read faster in Spanish, slower in Ukrainian).
Read/listen/watch 3000 words a day, understanding the majority of the words so you understand the whole passage, and after a year or so you'll be mostly fluent.
These figures line up with your 200-300 hours to read the Vulgate, as well.