Um, yeah. Your sources are either dramatic exaggerators or mostly making it up.
If you search you'll see live trip reports from September, October, November, December, January, February, and March. All of them chocked full of good things.
The things you mention are seriously in the minority of times. Cart parades are only like 3-4 times in a year and are a blast to get to watch. Otherwise, never an issue. There are the occasional bigger get togethers at some sites, we do hear of them from time to time but not enough for it to be an expected occurrence any more than other campgrounds you can visit. Multiple groups per site, you mostly find in the tent loops which are not premiums. There was a note of two campers on a same site back in January I believe, but again, not enough that you hear about it wrecking other campers times.
I stay at a lot of camp grounds from privately owned to Corp of Engineer, to National Park and the Fort was consistently the quietest of them all.
Of course, you can always get a resort room where you hear your neighbor flush the commode, their kid banging on the wall, people running up and down the hall outside your door or by your window on the outside walkway. You're good staying at the Fort. I'm not saying the group thing might not happen or that your neighbor might not have a get together, but it is rare we see it a problem.