The big issue that I found with the factory subie rack wasn't the towers or mounting points. The cross bars flex like wet noodles.
For anything wide and low profile, it would be perfectly OK. For anything high, with narrow footprints (like my Yakima Cobras), there is a lot of leverage. I don't have a sunroof on the GR, but could see the shadow of my bike while driving and the amount of side to side flex was shocking. Best guess was 5-6" in each direction, and I had the bike rack as far passenger side as it could go. I can only imagine how much flex there would be had I centered my bike.
Nothing broke, but I had no interest in testing fatigue strength.
Hicht mount is 10x easier to load (especially multiple bikes), underground parkades are a non issue, and I can see what's happening with the bike while driving. No brainer for big bikes IMO, especially since a hitch exists for the STI.