No, it's not proof at all actually. After the vast majority of their population was wiped out they embraced fel as a necessity. They'd have likely died out entirely if not for their use of demonic magic. Even the Alliance has since come to use it as a necessary evil - along with the undead and worgen who are arguably much more tainted and twisted than the blood elves - and the faction isn't even in a position where they're at risk of being wiped out entirely.
Attempts at reclaiming Silvermoon failed right up until Rommath arrived and used fel energy to restore the city to much of it's former glory. This allowed the blood elves to have a much greater chance of survival and they've since employed various pragmatic means to ensure that they aren't wiped out. Why would they roll over and allow themselves to be killed, especially after being betrayed by those who should have been there to aid them? Kael'thas had no responsibility to offer his aid to Lordaeron when his own homeland was in such a dire state yet he still had the decency to try and help the remnants of the Alliance.
Furthermore the use of fel energy is nowhere near as widespread as people try to paint it as being. They've since stopped using it as heavily and have embraced more efficient and pragmatic methods - which is very much where their story has been going for quite some time.