I think man on man would work better if your defence have more quality than opponent's attackers
Just think of it in live animation matches
Your defensive player would chase the attacker and manage to take the ball to start a counter attack but if attacker was stronger then your defence would become useless

However I hardly use man on man so I don't know how it really works in the game

I will try 4-5-1v hard defending long passes counter on and man on man tonight against much weaker team to see if it would give me more goals
I think the scenario : opponent attacker will enter the area then a defender would stand man on man and take the ball to start a counter then a goal ( opponent players are 2-3* and mine are 4-5-6* )