EXACTLY. Because Bean has little impact on that end of the floor. Put Duncan on that team in place of Bean and they win at least 50, rank much higher than last in defense, and make the second round. AT LEAST.
Now put Bean on that '02-'03 Spurs team and they look an awful lot like the Lakers in '04-'05
'03-'04 Miami Heat
C- Brian Grant
PF- Lamar Odom
SF- Caron Butler
SG- Eddie Jones
PG- Dwyane Wade (rookie season)
42-40 record (#9 Defense), beat NO 4-3 in first round, lost 4-2 in second round to Pacers
'04-'05 LA Lakers
C- Chris Mihm
PF- Lamar Odom
SF- Caron Butler
SG- Kobe Bryant (first year not playing w/ Shaq)
PG- Chucky Atkins
34-48 record (30th/30 in defense), missed the playoffs
Like I said, without at least an all star level big man Bean is a poor man's Allen Iverson.
Duncan easily has the bigger impact and is the greater player. The only advantage Bean holds is playing sidekick to the MDE.