all power to the leader

The political leader principle of all power to the leader, also known as absolute monarchy and best known in modern times as the German Fuehrerprinzip, googled, requires that all constitutional and legal norms be subordinate even to the whims of a party leader.

prevents ethics

In effect, the leader himself or herself is deemed to become a principle themselves, able to dismiss or de-emphasize other principles without recourse or remedy available to anyone who might object. For instance, no moral ordering could be imposed on other principles in a party with such a principle, since the leader could and would re-order them on demand, e.g. to achieve power or hold on to it.

Among most small or failed parties, the leader principle and associated beliefs (such as that meeting agendas must be set by the leader) are quite common. It might actually be responsible for parties failing or remaining small or failing to develop any ethic that people trust to make ethical tradeoffs they can accept.

Rushworth Kidder's definition of ethics as trading off right versus right, is incompatible with the leader principle in that explicit or rational justification of such tradeoffs cannot be required of an absolute monarch, who is assumed to have secret motives and knowledge that would endanger the state to reveal.

Machiavelli's fault?

Although Niccolo Machiavelli is sometimes blamed for originating or authorizing leader principle in The Prince, he was very clear in his earlier work The Discourses that there were necessarily limits on a prince's power including that of assassination when the prince had simply gone too far. His advice in The Prince is notably regarding only political and not military power, accordingly a Prince following Machiavelli's advice could be easily removed if they became a tyrant: they'd simply be assassinated. Machiavelli favoured constitutional monarchy with a recourse to the absolute only when facing rivals who did not obey the laws that he outlined in The Discourses - which in Renaissance Italy was most or all of them.

more than an autocrat

A person requiring all power to continue in the role is normally called a dictator.

Any more limited application of this principle, such as a belief that leaders should have all power but should be challenged by other leadership candidates once in a while, tends to be known by the term:autocrat. A corporatist philosophy tends to favour such people, emulating the substantial power granted to a corporate CEO, including that to change certain members of the corporate board of directors. Though not ever the Chairman of the Board.

In general people labelled autocrats tend to be insistent or bullying, but do not typically claim the power to wipe out whole peoples on a whim, as Fuehrerprinzip requires. See Godwin's Law for more on issues with comparing modern political behaviour to Nazis.