[Maédhros]

But then again, were the Gondothlim that strong? Because in BOLT Rog slays alot Balrogs.

The issue of Balrogs at the Fall of Gondolin is interesting. In the Tale of the Fall of Gondolin, there are hundreds of Balrogs.
From the Tale

yet others were creatures of pure flame that writhed like ropes of molten metal, and they brought to ruin whatever fabric they came nigh, and iron and stone melted before them and became as water, and upon them rode the Balrogs in hundreds; and these were the most dire of all those monsters which Melko devised against Gondolin.

But that conception changed of course:

ibid.
The idea that Morgoth disposed of a 'host' of Balrogs endured long, but in a late note my father said that only very few ever existed -- 'at most seven'.

So we have an evolution of the number of Balrogs. It appears that only Gothmog and the Balrog slained by Glorfindel were the ones who perished in the Tale and the others were to be discarded.

Regarding Rog:

ibid.
as the Noldoli sing yet, and many of the Orcs were borne backward into the fires below; but the men of Rog leapt even upon the coils of the serpents and came at those Balrogs and smote them grievously, for all they had whips of Same and claws of steel, and were in stature very great. They battered them into nought, or catching at their whips wielded these against them, that they tore them even as they had aforetime torn the Gnomes; and the number of Balrogs that perished was a marvel and dread to the hosts of Melko, for ere that day never had any of the Balrogs been slain by the hand of Elves or Men.

It seems to me that these balrogs cannot be taken to be of the later conception. In the examples of Echtelion and Glorfindel the Tale is especific by stating that it was a single Balrog, unlike with the case of the Men of Rog.
Also in the Tale, Tuor slew five balrogs too, which cannot be taken to be of the later conception IMO.