Djokovic has only been a leading player since 2007 - that is not quite 5 years. Edberg was a leading player from late 1985 (won Australian Open beating Lendl in semi's and Wilander in the final) to late 1994 (qualified for end of year championships) - 9 years. Becker was a leading player for 11 years (Wimbledon 1985 to Season end championship 1996), Wilander (from French Open 1982 to US Open 198
- more than 6 years. So he is coming up on Wilander but still a fair way behind the others.
He has 5 slams, Becker & Edberg are on 6, Wilander on 7. Becker won many season end finals and made the final match in many others too - so he has a great indoor CV. Djokovic is just won 1 - but it is fair to note that Edberg and Wilander aren't ahead of Djokovic there.
So I think he is still a tad behind them - but not much.