They were not mind controlled by Darkseid, they were possessed by the Furies of Apokolips
My mistake, I guess, but it wasn't made clear in the story, either. Yeah, Diana says "my furies", but I kind of assumed that was just standard Darkseid-ian terminology.
Do people honestly want to see all superheroes fighting crime in sweat pants?
Um, no (well, that would be a fun change if there was one hero in sweats). I honestly like most superhero costumes, including Wonder Woman's, surprisingly. It's just the little details in the art, like high heels, that really bug me. (And by "me", I mean me, and am not speaking for anyone else here or elsewhere.)
It's not the style aspect that bothers me (although Mary Marvel's attire is certainly hideous here) as the practicality of some of it. Like, okay, a superheroine's costume doesn't include pants or displays lots of cleavage? Fine, whatever. It may always be realistic and it may be an example of double standards in superhero comics, but I can deal with it. But when I imagine what it must be like to wear such a costume? If it would clearly result in a "wardrobe malfunction" or make it incredibly painful and slow to run (as with high heels), then that's where my suspension of disbelief ends.
On the other hand, if it fits with the character, maybe it can work. For instance, if a superhero is a supermodel in her day-job, she's probably used to wearing high heels the rest of the time, which means her leg muscles and posture may have become more adapted to that kind of shoe. In which case she may be just as comfortable in high heels as another woman would be in running shoes.
Like I said, this is just me. Mind you, it's the sheer uselessness of going out and changing your wardrobe once you turn evil that bugged me the most here. I mean, why bother? Why do they (or Darkseid) care? What is to be gained from it? Wouldn't they be deadlier if they were able to visibly pass for non-evil? What is the god damned point of it all? It's the lack of logic in the change that bothers me.
it's a few weeks after Final Crisis 3
Again, that was not obvious to me in reading it. (Granted, it's been a while since I read FC.)