This is not really true.
They can be gutloaded a variety of ways and were found to gutload calcium better than crickets when fed the exact same feed (according to ferguson- panther chameleons book. Ferguson used crickets and mealworms only to raise panthers over generations in his lab).
I recently posted a link with a nutritional analysis that found them similar to crickets in some ways, similar to superworms in others. Similar to other feeders in others.
That said, I agree with approximate percentages others here on the thread are recommending. Variety is the key.