5-3-2 is effectively 3-5-2 only it's when you've not got possession and turns to 3-5-2 when you have got the ball.
Except we know Johnson can't defend, so we're playing this formation for which reason again? Might as well just play 4-4-2 with him as a midfielder, which was my point. If you want 5 in the midfield (from 4-4-2) just allow the LB (or even Agger) to trot the ball up. Which was the point of my choice of Kelly so that we still have 3 players who are comfortable at CB in the back 4.