I'm on the SRT for at least part of my ride several times a week, love it! That being said, do not ride there if you want to maintain any kind of reasonable speed, as you found out, it's just too crowded (there are some areas away from downtown where you can open it up a bit safely). But if you keep that in mind, and just enjoy it, it's a nice way to get away from cars. I'll use it for recovery rides too, since it's about the only way to get a relatively flat ride in around here. lol
As a runner recently turned cyclist, I've found that many cyclists around here forget that it is the responsibility of the faster/passing party to pass safely, even if this means slowing down significantly. There are even Strava segments on the SRT, which is a little ridiculous, but that's life. It's especially annoying when the Hincapie Gran Fondo is going on and you get people running pacelines on the SRT.
If you're down this way again, there are lots of great group rides in the Greenville area, for all levels.
Oh, it's also Spring Break for this area, so that probably explains the amount of people on the trail during the day.