First, there is no centralisation of power simply because WHO doesn't have any power. Guidelines are not power.
Any influence (not power) they may have comes exclusively from trust. No trust == no influence.
Second, WHO cannot "denounce" itself, for the simple reason it would be against its overt mission.
The actual solution is to ensure integrity of the guidance that they are providing, which is necessary step to earn back the trust they have undermined.
When governments can trust the organization is science based and not steered by politics it can perform its mission, which is to provide guidance to countries and organisations that don't have resources to do it themselves.
Any influence (not power) they may have comes exclusively from trust. No trust == no influence.
Second, WHO cannot "denounce" itself, for the simple reason it would be against its overt mission.
The actual solution is to ensure integrity of the guidance that they are providing, which is necessary step to earn back the trust they have undermined.
When governments can trust the organization is science based and not steered by politics it can perform its mission, which is to provide guidance to countries and organisations that don't have resources to do it themselves.