No, he won MVPs because he's by far the greatest defensive player in league history.
Russell certainly has a commanding lead as the NBA's all time leader in Defensive Win Shares with a career total of 133.64, with Duncan 2nd all time at just 106.34
But Chamberlain is 5th all time in DWS with 93.92, so he's no slouch defensively either
Now, let's take a look at their Offensive Win Shares
Chamberlain's career OWS is 153. 34, which is 3rd all time behind KAJ and LeBron
Russell's career OWS is 29.9, which all time ranks... umm... uhh... I don't know because Basketball-Reference only lists the top 250 all time, and Russell ain't in it! To put that in perspective, Jonas Valanciunas is 223rd all time with a career mark of 41.95
Russell is currently 20th all time in Win Shares with 163.51
Chamberlain is 3rd all time at 247.26, behind only KAJ and LeBron
But since Chamberlain played significantly more career minutes, their career WS/48 will give us a more accurate representation of the on-court value they brought to their respective teams
Russell is 31st all time with .1927
Chamberlain is 3rd all time with .248, which trails only Jordan and David Robinson
And their single season high in WS/48?
Chamberlain's best season was .3251, which is the 3rd highest single season mark in league history, with KAJ owning the top 2 seasons
Russell's best season was .2384, which is 161st all time, and his only other appearance in the top 250 is 191st all time
Chamberlain has 9 seasons above Russell's single season best
So, even as the greatest defensive player by far in league history, Russell's on-court value to his team was considerably less than that which Chamberlain was contributing to his
The hockey equivalent might be something like Bourque vs Langway