Most of these projects that claim to have hit hard cap are just a sham. They make up this to lure more investors into the project. And even if they acually met hard cap, it's not a guarantee to the success of the project as you said.
Right now this is true since most of the ICO now are keep on claiming that they hit their hardcap, but still their project are down. Hardcap doesnt mean a good project, you have to look for the manipulation side and ask the community if they really see a good future with it. I have invested before, they hit the hardcap and yet its super cheap coins now luckily to sold it early with a small profit.