Solas yes, Flemeth no.There is no evidence to belive that Flemeth has more power than what she has shown so far.
Hardly, most of their power came from nature of the world that existed.Lack of veil would probably increase anyone's power, assuming they would survive.Plus, if darkspawn existed even before Elven gods still failed to defeat it.
The lore makes her out to be atleast the 2nd most powerful elven god, she pwned half of them in fights and exercised a good amount of influence over them before the betrayal. Shes definitly in the top 3 or 4.
And yet she considerd a recently awakened solas/dread wolf more capable of carrying out their plans by entrusting him with her own soul. Solas even states that she more or less did die, she just somehow saved a piece of her essence through sheer will for revenge.
To me, this hints that both Mythal and Solas, and the first elves elves in general, were definitly more powerful than what was shown so far.
Solas also hints that their are other ways to defeat the darkspawn other than grey wardens, so it seems the elves have not only defeated blights before, but they may have even used them.
And they don't just control nature, they control space and time practically.