According to Elrod Enchilada there are 13/14 Platinum Medal Superstars in league history.
1. Jordan
2. Russell
3. Kareem
4. Bird
5. Lebron
6a. Magic
6b. Pettit
8. Robinson
9a. Kobe
9b. Duncan
11. West
12. Chamberlain
13. Cousy
13a. Walton (not enough seasons so he was treated differently)
3 of the 13/14 platinum medal superstars are still active and there have never been more than 5 active at any given time (brief stint where West and Pettit overlapped with Russell, Cousy, and Wilt in the early 60's). The 80's also had 5 active for a few seasons because of Kareem's longevity, but he was far from the platinum medal superstar when Jordan entered the league (Walton was nothing more than a role player at that time as well).
If you add in Elrod's Gold Medal Superstars you get 5 more active players on the list and Shaq has only recently retired.
Basically, the league has as many top tier players now as it has at any time in history. There are just more teams and a lot of the talent is rising while the older guys are still around. Same thing happens every 10-15 years or so where Wilt/Russell give way to Kareem who gave way to Bird/Magic who gave way to Jordan who gave way to Kobe/Duncan who gave way to Lebron, etc.