My apologies, my response was unfair.
However, I still think 4 at the back suits the current Saints personnel. That season in the Championship under RM where we played 4 at the back was the only successful campaign under SR's ownership.
Playing 5 at the back requires 3 skilled, ball playing CBs which we don't possess. It requires good wing backs which we also don't possess.
The players we have suit 4 at the back rather than 5. THB, our best CB, is far more comfortable in that setup. It means we don't play the ball sideways and backwards so much. It means we have to play 2 proper full backs rather than pretend that Manning is a wing back and hamper Fellows who is clearly a winger not a defender.
Finally it allows us to play another midfielder or attacker, rather than Shoehorn a weak CB like Woods into the team.
Just my take ..