Don't take my word as law, but I owned a 2019 Les Paul Custom and now own a 2021 Les Paul Custom '68RI (as well as an R0 and a '61 from 2020 and 2021 respectively) and here is my experience....
The Les Paul Custom (for lack of a better word, the "standard" one) was an extremely well built guitar, of which I personally had no doubt was built by the custom shop. However, there were A LOT of finishing errors and the guitar was super heavy... I didn't weigh it, but I would say it was at least close to 11 lbs... weight relieved!
The guitar sounded great, pickups are rather hot... 498T clocks in around 14k DCR with Alnico V IIRC.
I sold the guitar and bought a '68 RI. IMO they didn't quite hit the whole T-TOP thing, but my take on the custom shop line as a whole is that the prime wood they receive (read lighter wood) go to the reissues, the more heavier and dense woods probably go to their "standard" custom shop lines. But this is only speculation. And while I find sonic merit in both heavy and light wood, if I wanted one that heavy, I would have just purchased a USA Classic.
I would venture to say that the overall structure quality was the same between the two. Though the RI has no weight relief and is under 9lbs.
I know that a lot of guitar companies do some rather dirty tricks. But I do not think this is the case here. What I will say however is that the more the custom shop expands... and they are quite a lot, the more similarities they will suffer to the USA shop. Again, just speculation and opinion.
I hope this helps to a degree.