I think if you understand the P=MC framework in terms of market power, it can be very informative! Or really it's the Marshallian framework in which MC is embedded, becomes the pivot point, that is informative. 1/

A flattish curve, high price elasticity, represents low bargaining power. The surplus differential, consumer vs producer, defined around the marginal cost pivot, reflects the average relative bargaining power of the two sides of the market. 2/

It's not a complete or universally applicable framework. Supply/demand curves are notoriously challenging to pin down in empirical practice, rather than in theory. The framework assumes single price markets, where much contempory market power is derived precisely from breaking that assumption. 3/

Still, where single-priced markets remain at least a somewhat reasonable approximation, I think Marshallian curves split at marginal cost remain a helpful way to visualize and think about market power. /fin