The decline in slam success was due to two factorsAverage height of top10s:
2003 - 183.3
2004 - 183.0
2005 - 181.7
2006 - 184.3
2007 - 182.7
2008 - 186.9
2009 - 188.2
2010 - 187.2
2011 - 185.9
2012 - 187.1
In 2003-07 Federer won 12 Slams.
In 2008-12 Federer won 5 Slams.
In 2003-07 he was taller than his main opponents.
In 2008-12 he was shorter than his main opponents.
How much did this affect Federer's results?
Slowing down of courts...specially at USO and wimbledon.
Facing to younger peak ATGs in his post prime version.
Still he was the only guy came close to goating peak djokovic by beating him once and coming very close for a 2nd time