There is a synergy effect: As teams get better, average players start to look better because they are surrounded with better players who either command attention (on offense) or who can pass or defend better. All of these things can help guys like Jerebko, Smart, Rozier to improve.
The opposite is true too. As good players leave teams, remaining players may struggle. Let's watch what happens to OKC, LAL and SAS. They each lost an elite player without anything in return. I bet a few of the remaining players struggle on each of those teams.