Actually this isn't the whole truth. There is a substantial body of literature around the effect of merging both positions or not and it is not really conclusiv

Actually this isn't the whole truth. There is a substantial body of literature around the effect of merging both positions or not and it is not really conclusive in any direction. You mention Europe but for instance in France it has been a corporate tradition too have both merged and separation has statistically lead to a significant underperformance. FYI it is called the agency vs stewardship theories and currently it seems like a academically the stewardship is slightly favored.