[Anguirel]

It's generally accepted that Balrogs come in two sizes-the size of Durin's Bane, and little ones conceived earlier in the Canon, larger than Orcs, but not massively powerful. The ones Tuor nailed at Gondolin were probably of the smaller variety; whereas, since Feanor was fighting Gothmog himself, the Balrog-train would have been the most powerful and deadly under Morgoth's command. So I'd say there is a difference between Tuor's feat and Feanor's.

About Feanor and Morgoth; Fingolfin was very much fey and berserk when he attacked; he had seen the realms of the Noldor utterly vanquished at the Bragollach. But granted Feanor was madder still. All the same, I don't think we should skirt so easily over the Valarin messenger's verdict:

"Valar he is, thou saist. Then thou hast sworn in vain, for none of the Valar canst thou overcome...within the halls of Ea, not though Eru whom thou namest had made thee thrice greater than thou art."

Of course, a possible interpretation could be that Morgoth is no long a Vala, as hinted by "thou saist".