So convincing Ar-Pharazon to attack Gil-Galad, while probably not being that hard, considering the dislike of the 'King's Men' for the Eldar, will actually be detrimental to building up a force strong enough to convince the king of Numenor he can sucessfully wage war on the Valar.
I doubt it; Ar-Pharazon would have waged war even if his fleet wasn't as great, due to the immense fear of death. Besides, I don't think destroying Gil-galad would have cost that much for Numenor.
On some other issues: why do you guys consider
Feanor to be superior to
Fingolfin in terms of arms? The Simarillion explicitly states that Fingolfin was better at combat, and even though Feanor was greatly enraged, Fingolfin was also capable of being furious (remember, when he rode to
Angband he was so great that he resembled
Orome himself). Their strengths are not directly comparable, since there is no account of how well Fingolfin did in fighting
Balrogs (or how well Feanor did in dueling
Morgoth), but I think we should go with what is explicitly stated (that Fingolfin was the mgihtiest in arms).
But of course, I agree that Feanor could have easily broken
Sauron. This is proved by a simple inequality: Feanor >
Ecthelion = Gothmog > Sauron. But then again, I highly doubt that Sauron would have stood in the way of Feanor. It's simply not Sauron's way; he did duel
Elendil and Gil-galad in the
Second Age but this time he isn't the final boss. It's more likely that he would have just fled or aided his master in other, more cerebral ways while letting Feanor challenge Morgoth directly.
As for Sauron vs. Gothmog... I agree that Sauron was a moe behind-the-scenes manipulator, while Gothmog was a battlefield captain and a warrior. My view, though, is that Gothmog probably didn't take any orders from Sauron. I see their relationship as more horizontal than vertical; i.e.
Melkor
l l l
Sauron Gothmog (
Glaurung )
rather than
Melkor
l
Sauron
l
Gothmog
l
....
So, they all took orders directly from Melkor, but Sauron just technically ranked higher than all others.
To address the original topic: I think it was
technically possible, but
practically impossible. What I mean is that there wasn't an intrisically insurmountable wall that prevented the
Elves from overthrwoing Morgoth in any way (unlike, say, if they were assailing
Eru himself). Fingolfin and Thorondor has proven that Melkor can be wounded (and that the wounds are not easily, if in any way, healed), and another inequality comes into play as well: a number of Balrogs >
Ungoliant > Morgoth (and we know that the strongest of the Elves could slay Balrogs). How many Balrogs were present, I do not know, and it could be that Morgoth was actually damn strong if we take the "thousand-Balrogs" hypothesis, but this, combined with the fact that he was wounded by Fingolfin and Thorondor, suggests that Morgoth wasn't all that great in physical strength. It seems logical to conclude that with sufficient force (say, a thousand soldiers plus a number of champions - Feanor, Fingolfin,
Glorfindel, Ecthelion, etc.), Melkor himself could have been taken under control in some way (imprisonment, destroying the physical body, sending him to
Valinor, etc.).
However, that is when dealing exclusively with Morgoth himself. He has a lot of minions -
orcs,
trolls,
wolves, Balrogs, and above all,
dragons. And he dwells within Angband, which provides a very strong home ground advantage. The
Noldor could at best form a siege, because the depths of Angband isn't exactly a good place to wage a war on. Meanwhile, Morgoth could build new
armies within his
fortress. Also, it appears that he builds them more quickly than the Elves, Men, and
Dwarves rebuild their, and Morgoth makes quicker technological advancements (what did the Eldar do when Morgoth was breeding dragons?). If the war ensues with each battle taking away the strength from both, Morgoth, whose army rebuilds more quickly, will eventually have the upper hand. Besides, I don't think the Elves, even with the fire-resistant Dwarves, could stand the
dragon fleet that Morgoth releases during the
War of Wrath.