Serie A Tables during Spalletti's Roma reign:
http://en.wikipedia.org/wiki/2005–06_Serie_A
http://en.wikipedia.org/wiki/2006–07_Serie_A
http://en.wikipedia.org/wiki/2007–08_Serie_A
2006 - 42 goals against (first season)
2007 - 34 goals against
2007-2008 - 37 goals against
2008-2009 - 61 goals against
The numbers are pretty consistent apart from his departure season, and in his middle two years his side was one of the top three defensively in the league. Inter was of course consistently slightly better.
During the good years, his overall record in Serie A was commendable.
But much of the whole "can't defend" argument stems from the European competitions where they kept getting trounced in the knockouts.
When you throw into consideration that these have been weak Serie A's over the years with Juve and Milan not being themselves after Calciopoli, you have to take these records with a grain of salt. Spalletti is an OK manager, but there are better managers out there. His squads tend to trend to the same loser mentality that he exhibits.
So... nay. We need better.