First up I don't really have an answer regarding who truly understands, or how does one, understand a kata.
In regards to the 'do' arts, the purpose isn't really about an end product. They are very much process oriented and immersive in an experiential sense as to what they entail. Tea ceremony or calligraphy isn't really about getting the perfect cup of tea, nor a nice picture afterwards. The end product is more a tail end 'sign' of the quality of engagement and sincere presence you held throughout the process.
In terms of kata, to me it's a tool for this same exploration. I'm trying very hard to not to sound too abstract or esoteric haha, but fostering a deeper mind-body connection, being immersed deeper in and experiencing the art's principles, and connecting to something far larger than yourself. You don't really 'get' anything in the end. Even the tea doesn't last, nor will the calligraphy piece last forever, same as the kata which I guess is more like music how quickly it's over.
That's probably where it gets confusing actually, the only real disconnect is when one camp is saying it's purely for the above, and the other camp saying it's purely practical, for self defense and has an end product. For me the kata must have a sense of realism and not just aesthetic (otherwise it would be a dance), but there is the opportunity to see it and train it as something deeper.
And yeah I find it more helpful to see kata not as a catalogue or alphabet, but as a particular tool for exploring the principles of the art.
Ah and the last question, I would say the person absolutely needs experience before benefitting. By that I mean practice under a teacher's guidance. If we're looking at practical application, when it works is the standard. In terms of a more 'do' perspective... no idea
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