Personally, I think it has led to people joining groups for the reason they should be joining - to team up and play with like minded people, not just to bring people on as prestige mules.
If poorly designed maps constitute a "unique challenge" and "fits thematically", then I do not know what to tell you. There is such a thing as bad design.
You have the benefit of hindsight here in knowing what to expect from the mission. Many others will not and again, poor map design exacerbates getting spawn camped.
To me, it is irrelevant whether someone can solo the mission or not. The issue is the placement of the spawn point inside the mission and that more often than not, players can consistently get spawn camped because of it. That is indicative of a bad design in my opinion. Other maps which have the hospital in the mission allow the player to collect themselves in safety.
Yes, I understand all of this. I understand Superman is not intended to be as flawed as your average human. Trust me, I get it. However, by magical means or some other outside influence, Superman can be forced to do something against his will. Or are you suggesting he can be forced to sneeze only?