For Italian, I took an official B1 exam in person in Seattle almost exactly one year ago and passed easily. At that time, my LingQ stats were obviously much lower (I had about 20k known words, 25 hours of speaking, and 1 million words read, including reading done before I started with LingQ). With that in mind, it doesn’t seem unreasonable to assume that one could be very proficient in a language at 2-3 millions words read, 40-50 hours of speaking, and 35-40k known words. This also assumes that B2 is the threshold for being proficient/fluent, but obviously some people may have lesser or greater goals.
Now, have I reached this point? I think that’s a hard maybe.
After about 2 million words read (this includes time spent reading before I found LingQ), I can read books unassisted now, though I’ll still come across unknown words. However, 95% of the time, that unknown word doesn’t impact my ability to understand the passage.
I don’t practice writing through any kind of concentrated practice, though at the B1 exam 1 year ago, I obviously passed the writing portion at that time.
After ~300 hours of listening, I can easily watch youtube videos, listen to podcasts, watch/listen to the news, watch most movies/tv shows without subtitles, etc. However, some movies/shows are much harder than others due to dialects/accents. So, I’ve still got a lot of practice to do there (probably minimum 100 more hours).
Finally, I have conversed many times with language partners in only Italian for well over an hour, and apart from pausing every once in a while to think of a word, or sometimes asking for help thinking of a word, it’s been very fluid.
Basically, I think I’m close to that point that you describe wanting to reach, but not quite. So, my statistics may be a good estimate on the very low end of what’s required, but obviously there are many other extremely active users on LingQ whose statistics may tell a completely different story.