4Ps are Not Optional, but Key Issues that MUST be addressed
The concept of a Marketing Mix implies that these are not options. In practice the 4Ps represent the key questions or issues that need to always be addressed in Marketing. There is no trade-off among them. They are each key action issues.
There are a number of other issues such as the participants referred to as the 4Cs and the marketing concepts which would include segments, offerings, brands, position and value which are used to formulate strategy and development the actions.
But the 4Ps remain as the underlying key issues that need to be addressed.