More teams = more parity. While Kobe and LeBron faced the same amount of teams, they played during the "superteam" era when players tried to latch on with other stars to increase their chances of winning. Not as much top-to-bottom competition.
More teams eventually equals parity. However, it doesn't equal parity right away because it takes a few years for the overall talent to catch back up.
I agree about the superteam era for Kobe and Lebron. However, I think it doesn't change much re: what they have faced vs. what MJ faced. MJ was in a watered down league, so while many of the top teams were still really good, there were also a lot of average to below average teams to beat up on.
In the superteam era (which seems to be slowing down some) there was a little tougher competition at the top of league, but still plenty of average and below average teams.
Now, over the past couple of seasons, we are seeing more parity than before because players are looking for places where they can win, but not necessarily looking to form superteams. The result is that there are now really only 3 truly bad teams. Maybe 4 as the Suns seem to gone into the tank with the Bledsoe injury.