User blog comment:FairyRaven/Fairy Tail Chapter 391: Gray vs. Silver, Review and Commentary/@comment-24784846-20140704210129/@comment-7418318-20140705141307

I'm not saying that Tartaros ever fougth against other Demons, especially not the weaklings on Galuna Island.

We haven't even seen half of Fiore and even Fiore itself is a comparetively small country on this one continent, but there are other continents and even other dimensions where more natural Demons might live and war.

Maybe Silviora didn't make a move on Lyon while Gray was frozen because he had to go on a far journey to one of those other Demon tribes and wrest the secret of Demon Slaying Magic from them (I'd like that if it was true).

As for the power-balance, even with that magic Silviora still won't be an equal to Mard Geer. If the leader is so much stronger than the subordinates, you don't need a balance of power among the subordinates. Franmalth ability would already put him above all the others - except for Silver himself obviously - if that wasn't the case, unless he can only absorb magic but not curses.