Honestly, I think all GravityKraft does is do what the parks were doing before, which is go out and hire the people to build the ride. I don't think they actually have a crew like GCI does. They hire the people, and then send one of their engineers out to oversee the project.
To me, track work is probably the most important element to a wooden roller coaster being smooth. The bogie POV of Mine Blower was mentioned. That ride has poor track work. If you look at that POV, watch the train go up the lift hill. The reason the bogie system bounces back and forth is because the the lift track isn't straight. When GCI builds a coaster, they build one side of the track first, then measure across to build the other side of the track so it's precisely built to what it supposed to be. Gravity Group rides are more old school, where they lay the track and then make the cuts kinda of eyeballing it. If someone's doing the track work, and they don't have a whole lot of experience, it's probably not going to be very good. In Mind Blower's case, you look at how quickly they got that ride up, that seems to tell me that the whole thing was rushed.
While were on the subject of track work. I find it interesting that Holiday World is using suggestions from The Gravity Group to make track improvements to The Voyage this off-season while using track building techniques they learned from GCI during The Legend's refurb to lay the new track.