Not really concerned about the defense, I think it's hyperbole and mostly denial/fear from non-Spurs fans..losing Splitter hurts, but Aldridge is an above average defender and Green's increase in playing time(which is virtually guaranteed with Ginobili's decline in minutes and Belinelli's absence) will help offset any defensive drop-off..
I've seen some silly comments regarding the Spurs' bench, too
..there's no reason to think they won't be one of the better units in the league..
My biggest and only concern is playmaking from the perimeter players, particularly Ginobili's remaining ability and whether Parker accepts a new role or not..it's a huge concern and by far the biggest question mark..