High Elves and the Balrogs

[Gorthaur the Cruel]

I know the Balrogs were of the Maiar, but it seems unbelievable that a mere high elf like Ecthelion and Glorfindel could've slain them (more unbelievable is Echthelion who was able to slay 3 Balrogs!). Why is this? Were the maia that joined Morgoth extremely weak that a high elf can slay them? I don't understand because Balrogs are great spellcasters and just totally on a different level. Would this mean that someone like Galadriel could take on that Balrog in Moria even without Nenya? 'Cause it would make sense since she's a high elf and the greatest next to Feanor. And where do the spirits of the Balrog go when they die?