There's nothing wrong with wordless understanding per se; the thing that's "wrong" is thinking that you have words (i.e. a teaching) that can effectively, repeatably communicate a concept, when you actually just have a wordless understanding.
The problem of meditation teaching is false positives: people experience enlightenment while pondering some koan, so they think that that koan actually helped, and pass it on. It's superstition. Anything could have helped. Something that truly helps, should help more people than average, more often than chance—and if you've got that, you've got words.
False dichotomy. Understandings aren't completely wordless or wordable. They fall along a scale.
> Anything could have helped.
If something helped a person, and they want to pass it along, even if it's difficult to communicate in a tangible fashion, I'm not going to stand in their way.
Sure, but If I want to learn a difficult-to-communicate lesson, I would hope that the people who have a wordless understanding would keep their communicating to themselves—unless-and-until they come up with some coherent words to match their thoughts, that they can be sure can be used to reconstruct those thoughts without their brain there to help.
People don't yet know what they don't know, until they know it—so it can't be the learner's task to preemptively avoid vacuous lessons. That responsibility has to fall to the teacher.
The problem of meditation teaching is false positives: people experience enlightenment while pondering some koan, so they think that that koan actually helped, and pass it on. It's superstition. Anything could have helped. Something that truly helps, should help more people than average, more often than chance—and if you've got that, you've got words.