There are predictable results when senior leaders push too hard on too many things.
Cynicism. Because you cannot do everything at once, leaders who are always pushing for more and for better eventually wear their subordinates out until each new proposal is met with a certain level of skepticism, even cynicism. Better a few important initiatives than many minor ones. More does not equal better. Usually it equals mediocrity. Usually, leaders who push and push also change their minds often leaving staff who have worked on an initiative frustrated when they must change directions mid stream.
Discouragement. There is nothing better than celebrating success. But when many initiatives are on the plate, success is elusive since most will not get accomplished. Or accomplished well. This is discouraging to staff who are working hard to accomplish the mission of the organization.
Lack of focus. None of us can focus on more than a few important issues at a time. When leaders make unrealistic demands on many fronts, staff don't know where to put their energies and the priority of the senior leader my change quickly. Staff are left to guess as to which initiative is the priority leading to a lack of focus throughout the organization.
Commitments that don't get kept. When pushed hard, many staff will make commitments that they don't want to make and cannot keep. It is the only way to relieve the pressure of the senior leader, however, so they do it. Many of these will not be met because they were unrealistic to start with. This then sets up a cycle of blame for promises not kept which in this case is the fault of the leader rather than the staff member.
If senior leaders will allow their senior team to have a voice in what issues are tackled when there will be a far more realistic view of what can and cannot get done and by when. When leaders exert too much pressure they hurt themselves, the organization and the staff.