Thanks for your question. In reality, when using the CDH the way to go is to create offers (actually in 8.3 called Actions) and not propositions. As you have indeed noticed when you create an offer, the underlying proposition is automatically created for you.
Also moving forward, in 8.3, when using the new NBA Designer, all eligibility, applicability and suitability rules can be defined at Action level directly. So we are transitioning from propositions to Actions defined in CDH/Pega Marketing.