During the Windstop, initiates of Orlanth and Ernalda within the affected area could not use their Rune Point pools to those gods and subcults of those gods. That includes Orlanth Adventurous, Rex, Thunderous, and Vinga.
Tatius the Bright expected that it would cause the Orlanth cult to collapse, but instead, Orlanth’s associates stepped into the gap. Chalana Arroy, Eurmal, Issaries, Lhankor Mhy, Storm Bull, Maran Gor, Babeester Gor, Grain Goddesses, and many others (including friendly cults such as Humakt) took on a greater social and magical prominence during that year. When the Windstop ended, the respect for the Orlanth and Ernalda cults actually rose as their importance in maintaining the cosmos was made more vivid.
Now part of the reason the default setting is moved to after the Dragonrise is that the Windstop is IMO better handled in retrospective. We didn’t think the default campaign path should be to make up a character in either of the two most popular player character cults and shortly after be told, “Sorry, none of your magic works.” And then keep that up for another three seasons or so. Obviously, if you want to play that, do it. But we concluded it was a far better idea to put that and the Dragonrise in the near past, and move forward from there.
Would the “biggest” mistake (by Tatius) have been to include Ernalda in it? Arguably the biggest mistake was to decide to massively change the mythic structure of Glorantha in the first place.