Data model agnosticism has nothing to do with the “emergence/popularity of non-relational technologies” (NoSQL, NewSQL did not exist when Chen introduced the E/RM in the 70's), it is is inherent in conceptual modeling--which is what E/RM is used for--by definition. Conceptual models are expressed in real world terms--facts about classes of property-sharing entities. To be represented in a database, a conceptual model must be formalized as a logical model expressed in database terms. That's when a data model comes into play, to provide abstract data structure, integrity and manipulation (relation, relational constraints and relational algebra in the relational case). The conceptual and logical were always separate, but as Everest comments show, levels of representation are constantly confused.
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