Why do firms bother to produce at equilibrium quantities if at equilibrium quantity, MR < MC?
The MC curve can only be seen as a supply schedule for the individual firm if it is a price taker. In the case you depicted, however, we have imperfect competition. A profit-maximizing firm will thus produce where MR=MC, and charge a price that will induce consumers to purchase this quantity (which can be read off the demand schedule). In this sense, there is no "disequilibrium": the firm is doing the best it can (so it has no reason to change), and total quantity demanded is equal to total quantity supplied (i.e. there is market equilibrium).