If a learned person has the choice of learning something by themselves that they never learned before and going in depth into it, vs learning with someone who otherwise wouldn’t learn but you’d be learning something basic that you already know, what would our rabbis suggest to do? Focus in yourself and grow your knowledge, or learn with the other person, even if it’ll be low level, and thus imbue some Torah into his life?
R Moshe Feinstein has a teshuva (EH 4:24:4, right side of here, about mid-page) where he writes that a talmid chacham should spend a portion of his time teaching others, even if it means giving up some of his own learning. He writes this is for sure 10% of this time, possibly up to 20%.
R Moshe finds a proof in the gemara (Eruvin 54b) where R Perida taught one of his student 400 times the same lesson, and mentions this was for sure in the time he was giving others.
See also this broader essay on the topic from 1973 which I scanned for MY.