I think although TGC does in fact employ unity as the engine, GNCD is a tool in it's own right and is not subject to the unity platform, GNCD is a fun tool but lacks the versatility of CF. Quite a few of the established designers over at TGC are churning out courses that are very much like their previous efforts due to GNCD's limitations, the new textures are a help but they only gloss over surface nothing else, and when you do try something different you get poorly rated by people who simply have no idea about course design. I published a track recently that employed undulating greens with a slower green speed to accommodate and it gets rated down badly, as soon as i flatten them out, increase the speed and release in a different theme it gets highly rated! these are the kind of clueless people you have to deal with over at TGC i'm afraid, if they can't shoot the lights out they rate it down, lol and some just rate down out of spite because i'm not mr popular over there sadly!
It is indeed an odd occurrence, but that seems to be the lie of the land with golf games.
I think this so why some folks are quick to post negative things about PG after only playing the game a handful for minutes. Because they can't get a grip on the control mechanisms and in game physics, they are unable to shoot in the 50's like they would have in Links and TW, so say the game is flawed. In the same way someone designs a course with a bit of a challenge and different to the norm in TGC and it gets panned. Tweak it, and remove some of the challenge and the 'go low' brigade suddenly love it, lol.
BTW, I'm in no way saying PG is flawless, as we all know there are bugs and minor issues to resolve and I'm sure in time we we will see many resolved and the game grow.