As far as im aware yes concentrate on defensive & physical for midfield and defence while it's offensive & physical for strikers...
But...
You also need to add some skill to their weaker areas so that the players overall skill level improves...
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Don't forget there needed to be a 20 point balance!
As one of my Strikers keeps passing to my defenders instead of shooting, I am starting to add skill points to attacking/finishing to all my defenders.....
If you have e.g. 40q on attack and 20q on defense, the game won't let you add more skill points into the attacking qualities until you raise the player's defensive ones.
On topic - the only thing that I've observed in my players is that those of them who have low defensive skills tend to get more yellow cards, especially for the MCs - I have one that already got suspended twice in the league (+ he has another yellow now), once in the cup and will miss the CL final due to another suspension.
I have a DL who has a "corner kick" SA, but wasn't very good, until.....2 seasons back, I started putting all his skill points into his attacking category (where the crossing skill is). Since then, in the last two seasons he has "assisted" in 19 and 16 goals respectively. And he is my weakest and oldest player at the club.