Mathers did the work. Whatever the order's founding fiction, the rituals, the grade structure, the Rose Cross and the elaborate synthesis of Kabbalah, tarot, astrology, geomancy and Enochian material into one graded curriculum are largely his construction, and they have outlasted every organisation that has carried them.
He was also a translator of real consequence, though an uneven one. His Kabbalah Unveiled (1887) works from Knorr von Rosenroth's Latin rather than the Aramaic, which limits it. His Key of Solomon (1889) and Book of the Sacred Magic of Abramelin the Mage (1898) put grimoire material into English for the first time in a usable form. The Abramelin translation in particular shaped a century of practice, Crowley organised his entire early magical career around its operation, and it was made from a single defective French manuscript in Paris rather than from the older and fuller German originals, a limitation not generally known to the people who worked the system from it.
The titles are a different matter. He styled himself MacGregor and later Comte de Glenstrae, claiming Highland Jacobite descent; the family was not Highland and the county title has no basis. Like Westcott's German adept, it is a claimed authority with nothing behind it, and it belongs in the record next to the genuine achievement rather than instead of it. His autocracy and the disputed authority of his own Secret Chiefs broke the order apart in 1900.