Khm, I don't know how, but seems whole our server has about 5-7 sylphi's.
About 5 in one guild, another one in other guild and maybe few on lower levels.
In second top guild we don't have any
so merc camp does not work really. Even if we had one, it is unlikely to achieve a lot on hol with only one try.
By the way, hol is not much different to arena, it is competition for soulstones of very important heroes.
So when legendary kong is in HoL all syplhi owners occupy top7. Other bosses is more or less possible to get high score without her, still she gives good advantage, and as I understand this difference will only grow in future.
That's really what spoils game experience.
She is still very good in arena, I would compare to firehawk for usefulness. So one more strong hero for epic.
Thats why she is much more annoying than lingling, who also raid/hol hero, but at least very situational in arena.