How was it terrible other than no way to reset the fight? It was a pretty cool fight that REQUIRED people to actually take a second to discuss a game plan to succeed. But again that's too much for people to do in gaming theses days.
And that's exactly why it was terrible. Stuff that's difficult enough to the point where the DF usually can't do it is not something that should gatekeep an entire expansion. It would be as asinine to me as making a fight like Titan EX the requirement to getting into Ishgard instead, and that's basically what pre-nerf SoF was like for me in terms of how often you'd get a win on it on the DF.

When pre-nerf SoF was put on the trials roulette, I stopped doing that roulette for a while because the roulette landed on it the vast majority of the time, and the vast majority of the time it would be a group that could not clear the content, so why waste my time?

The initial fight left such a sour taste in many players' mouths, to this day I still very often get people who immediately leave the group when they land in SoF as their roulette, even though nowadays the fight is pretty much pathetically easy to clear. I don't think many even realize that it was nerfed.