That makes no sense. Alessia blended Mer and Men pantheons. Wulfharth wanted to wipe out all elves completely and utterly. How does it amount to Alessia being worse? It makes no logical sense.
Because Alessia herself had nothing to do with the Alessian Order, aside from appearing in a vision. She herself did not found it. Instead, a priest named Marukh did several hundred years after Alessia's death.
No where is it said Wulfharth wanted to wipe out all elves. He hated the Dunmer, yes, but his views on elves is never expanded on.
This monotheistic religion was once very popular, but today only remnants of its faith remain. It started in the coastal jungle of what is now the Colovian west, where a prophet named Marukh, who had spoken to the "Enlightened One," Saint Alessia, began to question the validity of Elven rule. These sentiments led to an increasingly abstract and unknowable depiction of a Single God. The Alessians were wise enough to realize that they had to incorporate the ancient polytheistic elements into their new religion for it to find a wide acceptance. The divine aspects worshipped by the various humans and Aldmeri were recognizable in the guise of the myriad saints and spirits of the evolving Alessian canon. It wasn't long before the Order was the authority on every religion in Tamriel, and their power grew to earthshaking proportions. Nearly a third of the First Era passed under their theocratic rule. When its priesthood had become too widespread to support itself, the Order began to fight among itself. With the severance of the territories of West Cyrodiil from the Empire, too much money and land had been lost. The War of Righteousness broke out, and the Order which had almost ruled the world undid itself in a ten year span.Read http://www.imperial-library.info/content/pocket-guide-empire-first-edition-cyrodiil, please.
Hmmm... I can't seem to find anything on the Alessians being genocidal. They didn't like elves, but nothing on purges right now. I take that point back.
Anyway, the Alessian Order is not the Alessian pantheon.