That is not even close to being true at all. Size wise for the scale of certain sets, Gothic works better in a SS, but its not 100% necessary. Any "flying scareactor" type effect is only possible in a Soundstage, same for certain visual effects (although thats debateable). Cabin in the Woods could easily be the Terror Tram or a park-wide SZ (a REAL park-wide SZ, not 3 designated SZs in the park... yea, i'm looking at you 2016's Purge). Nightengales most certainly did NOT require a soundstage, you were in war trenches. Not exactly a lot of height required. The only thing that required the use of a SS was the flying scareactor effect.
You can't judge a maze by how many IPs it has. There is a good possibility that Orlando's Blumhouse of Horrors will wipe the floor with ours & flush it down the toilet. Its essentially the same as sharing a singular IP... They may be similar, but execution-wise, they are drastically different. And while one might have more/different IPs than the other, does not mean it will be better than the other.
Tents work better for most stuff? What?
That doesn't even make sense. That is exactly the same thing as saying mazes are better in Soundstages (which you originally stated). Orlando has had mazes in ride queues that were better than a SS maze. Hell, they've even used a restuarant & the empty interior of a NY facade to have a maze. Its all about execution, not location or if its under a tent or not.
AHS mashup doesn't work because a season ends up being too small? Thats not true at all, Thats like saying Blumhouse of Horrors doesn't work because certain IPs get ____ # of scenes. Or if we want to go back to Orlando, who has had MULTIPLE mazes over the years featuring multiple IPs- House/Museum of Horrors, All Nite Die-In, Silver Screams, etc. It all comes down to execution, not necessarily location.