[Lindale]

Melkor is a good strategist, but he isn't the best. He did achieve to sow discord amongst the Noldor under the very nose of the Valar, and that for me is either a huge feat or the Valar were just too stupid. And the thing with Hurin and his kin. However I think there are things Melkor overlooked, like Beren and Luthien, and there are stuff that he didn't plan that just worked for him, like the Kinslaying of Feanor and the curse and other discords among the Noldor that followed.

He saw that he didn't need to attack Melian, as Melian did nothing to oppose him other than guard her realm, Melian was no threat to him. I mean, before the time of the Noldor the Elves of Doriath didn't go to open war or march against Angband. And what purpose would Melkor get? He probably foresaw the discord that shall follow the Kinslaying, as a proof that he still had a measure of wisdom. If he attacked Melian and Doriath that would be a good reason for the Doriath Sindar to forge an alliance with the Noldor even just for the sake of having a common great enemy, either if he attacked before or after the Noldor came, because I think that it would take a lot to destroy all the Sindar--he still had only orcs and no dragons till after the Noldor arrived.