It's called a sophomore slump. A lot of second year players have it.
It could be; however, teams now have a whole year's worth of film on him, division teams have two full games playing against him as well. OCs around the league will be "scheming" against him, IF he "slumps" this year, it may be that rather than Parsons himself.
But of course, not every second-year player has a "slump", I'd choose to remain optimistic that he won't. With a key defensive draft pick, another off season for Diggs and others, as well as (hopefully) a good defensive draft pick, Parsons might not even need to be better, or even as good, for the team to do better.
Oh well, will be something to watch....