Yes, learning new content with the language is key. Laddering is a term used when you are learning a new 3rd language through your 2nd language. For example, learning French through French for Spanish speakers-type material.
The 80/90% comprehension ballpark figure was more about how much you can understand without looking it up. For example, when I watch a reality TV show like Gran Hermano (Big Brother reality TV series) where there is a lot of regional accents, rapid-fire repartee, idioms, street talk, I can struggle to figure out what was just said. The same goes for a standup comedy show in Spanish with the cultural contexts, inside jokes. On the opposite end of comprehension would be an evening news program where everything is said in a structured manner and the diction is as close to neutral/perfect for the greater region of the news broadcast.
Additionally, the environment matters. A crowded noisy bar can rapidly beat up your confidence of being able to communicate. The Foreign Service foreign language ability scales do account for this.
Key insight, people should set the realistic goal of being at most as good as their native language.
I can confidently say, in my native language, there are many times throughout daily life where I have way less than 80/90% comprehension. The other key insight though is that I can remove that ambiguity with follow up questions and elaboration if I want.
And that's what people should strive for when learning a second language. Once you get to the point where you can learn in and with the language, then you're golden. That requires far far less effort than most people estimate.