Dwight is only 25 and has a significant amount of room for improvement.
That was true about 20 years ago when people were coming out of college at 22-23. With kids coming out at 18-19.... 25 is relatively "old" in terms of basketball at the NBA level.
He may not be maxed out. But he is pretty close to getting there. After all, next year will be his 8th(!) season.