I think Somebody and nick both have good points on TS% vs rTS%.
To support nick's point, look at the 2014-2016 seasons in TS%.
2014 .541
2015 .534
2016 .541
If a guy had a slightly fluky 3 point percentage in 2015, using rTS% as a metric would overstate him as being very efficient that year even more than he already would be overstated. There wasn't some real thing affecting league efficiency in 2015. It was just normal variation.
Similarly, Carter's rTS% is 0.5% higher in 2001 than it would have been had he had that exact season in 2000. Should it be considered as legitimately such? Probably not, IMO.
However, I think there is an actual difference between scoring efficiency in Carter's era and Westbrook's era that should be taken into consideration. I was the one who equated the two players in a PM and while I still don't see them as hugely different, I definitely now recognize a difference worth being mindful of.