The 3-5-2 is determined by the recruitment, Collins is there to coach it. I don't believe Collins or any other head coach would be able to rock up to training and decide this week we're playing 4-4-2. That's the point of the analytics, we recruit players we think can play in a specific system, if you read the job spec for the DOF it's for them to determine and implement that system across the club.
Love 442 or 433 but the problem is Mael and McCart are not strong enough as a 2 and no natural left back.