I've never loaded a 6 xc but other than BR based cartridges the 6 GT is the easiest cartridge I've ever loaded for. In load development at 150 or 200 yards it rarely shot anything over .5 MOA, wide nodes around .3 MOA were the norm without any real tuning outside of powder and seating, no neck tension test, no primer test, no checking different bullets etc. I found myself picking charge weights and seating depths off shape and POI more than size because the nodes were so wide and forgiving.Just my opinion, the 6GT is a tweener that doesn't seem to be very good at anything. It only has one source of brass. And that source could dry up at any moment. I'm pretty sure you could soft shoot the 6XC and it would smoke the 6gt and the 6XC will literally feed out of anything made for a 308.
For you to say "it's doesn't seem to be very good at anything" makes me wonder if you've even tried one? Then you say "you could soft shoot the 6xc and it would smoke the 6 GT" and I wonder what you're using for a yardstick?
I don't pretend to speak for Tom or George and have no experience with the xc so I have no opinions on it but I don't really believe the two cartridges were designed with the same goals in mind but that's just my opinion.