I think there is a defect in the redesign implementation.
At season start, the sum of design points of the car is divided until at a maximum value of 50% (with a 5* staff, both CD and DT).
With a 4.5*, the sum is calculated on a 90% of the sum of all areas.
So, we have a 43% in major number of cases.
But there is something missing: the percentage doesn't take care of the level of the staff compared to the manager's level.
To be more clear, if your manager is on level 18, with staff at level 18, the redesign will be the same of a level 18 manager with staff of level 17.
This is wrong! Many managers decide to keep their Chief Designer even when they pass a level, because it's too difficult to find another Chief Designer with good strength and/or good weakness.
So, at season start a level 17 staff of a level 18 manager will develope a car with same design points of a level 18 manager with level 18 staff.
The result is easy: the Chief Designer is too important with the right strength and weakness.
My suggest is to add the proportion of staff Level compared to the manager Level, so that a level 17 staff will not be any more stronger than a level 18 staff.
So, with a 4.5* staff, the division must to be calculated also by the manager's level: to be more precise, this is the formula I suggest:
Sum of points * (number of stars / 5) * (staff level / manager level)