"not the First" so said mandos. Personally I think it was hyperbole. He would have been chastened in spirit. and perhaps forged to a higher sheen. But my original thought was that the ages beyond the third would never have taken place. The music of the ainur would have been cut short on a foul note had feanor been complacent. and would have served melkor ultimately buy complying to the valar. this would have Allowed morgoth the time to subjugate the world to his will while the valar tarry beyond the boundaries of the mortal world. Melian and Thingol would be overwhelmed thus no beren and luthien no Tuor and no Aragorn.
Fingolfin perhaps would have been emboldend but he would not circumvent the will of manwe as he percieved it. emphasis on percieve. (fingolfin my fav).
Please forgive misspelling
