Doing a reread of WotSQ for my Drow campaign.
Using OotA as source material. Thought about running it. It's not good.
Yes, I wouldn't advise the OP to run it as written. More as source material - great maps, many interesting NPCs, several useful set pieces. It underpinned an enjoyable two years of gaming for my group of six PCs, so we got excellent value on the purchase. We ran from the book start (imprisoned) to a variation on the end scene (as one might expect, given all that can come between).
It is important to decide what you want from the demonic incursion. In my campaign, I thought about the strategic and political implications and put things in motion accordingly. That took our narrative well away from the elements
@Charlaquin didn't enjoy or found repetitive. The journey of my group through the Underdark was more a challenge in managing the opposite: a very great diversity.
Take the criticism of disastrous events that can't be avoided or prevented. The setting is cataclysmic. The demon princes are overwhelmingly powerful. So in that sense absolutely - how could the starting PCs or even the mid-campaign party possibly oppose them!? Except for the first scene with demogorgon (which announces the incursion and I felt just had to be retained) I made it a topic of urgent concern for denizens of the Underdark to have some idea where the demon princes were, with much speculation as to what they were up to. Standard foreshadowing really.
So there was much avoiding done on the part of the PCs. The payoff of course is in the turn-about: when finally they prevailed. If the demons were not so threatening, not so overwhelming for so much of the time, I think that just dilutes the narrative. "
We beat a thing, that we were guaranteed to beat, and that we were able to avoid or prevent all the way through" - a challenge with these published adventures is to create a sense of doubt in the conclusion. And on the other hand, a DM needs to be sensitive to the nuances - the wedding is not the same at all as the creeping insanity in Gracklstugh - and even more different if you can distil for your players something about the difference in outlooks of the fungus people and the deep dwarves.