This is a useful but problematic analogy. If you do language immersion, you are learning the language as it is spoken by a community of speakers. Generally, the worst thing that can happen is that you learn an unfashionable dialect and people make fun of you.
If you learn to DM by doing, the 'community of speakers' is your own table. We see this problem all the time, including in threads like these: everyone is speaking 'D&D', but no-one can understand each other. We're all mostly speaking gibberish and reinventing the wheel. This problem is probably insoluble, but a responsible approach to teaching would try and establish some kind of baseline.
One interesting point in which the analogy works is that, in my experience and many other people's, immersion learning tends to plateau after a while. Those much-maligned grammars and dictionaries are important learning tools that remain useful to advanced speakers.