Dragons vs Balrogs

Glaurung was young when Fingon drove him back. No Balrog is ever "driven back" in The Silmarillion. And the tales of Balrogs being slain at Gondolin are non-canonical, as Christopher Tolkien went all the way back to The Book of Lost Tales to write that chapter. He had no way of knowing (as we have no way of knowing) what his father would have done with the story of Gondolin after Tuor reached the seventh gate.

It is very probable, however, that NO Balrogs would have died at Gondolin, had J.R.R. Tolkien finished rewriting the story. He had already decided, by the time he started work on "Of Tuor and his Coming to Gondolin", that there had probably only been 7 Balrogs at most.

In "The Fall of Gondolin" there were at least 1,000 Balrogs. They were fierce and terrible warriors, but they were not the fallen angelic Maiar of the later Silmarillion.