This is not completely wrong, though I am not sure that those you would consider mysticists, understand philosophical idealism (not the same as political idealism, though there are similarities). The sceptical idealist, both realises that what you experience, is not what the things are in themselves, but tat the same time has the humility to say, that "metaphysical" realm, is beyond knowledge. The mysticists you refer to could be classified as those who want you to dismiss any kind of knowledge and then tell you what you should believe, and that would be whatever they want to be "true", conjured up in their sophistic mind.