While you're free to discuss what you think would balance Monster as a pack to be played in a fashion akin to other packs; Jaded has quite plainly stated before that Monster is the pack designed by slowpoke to go with the challenge map. Mods in it are in it specifically for the challenge map aside from BoP/ATG/etc(I assume) which won't have any effect on the map whatsoever(Again I assume) but make it playable as a pack in its own right. The challenge map, as Jaded has said, will be what is used to balance the mods in Monster by gating what you're able to craft, use, farm, etc.
Yes, the pack is mainly designed with the challenge map in mind. But lets face it, it does also serve a secondary purpose(IMO in all practicality a much greater purpose) of being a pack that is distributed for people to play.
As the pack comes it contains a number of mods disabled by default already. Now if slowpoke really wanted those mods in the pack why are they disabled? And if slowpoke didn't want them, why are they in at all? Obviously concerns of the users of the pack were made here as well. Not just what slowpoke wanted in the challenge map.
So I would think it would be completely fair to discuss why it wouldn't be logical from a users point of view to have say dyetrees disabled by default, when something like MeteroCraft is. Or EnderNet vs. qCraft.
What is the de facto 1.6.4 FTB balanced pack then? The others are all specialized (tech-based, difficulty-based) with the exception of DW20
I don't think we should take this so literal. After all Ultimate and Unleashed were also packs tailored for the use in challenge maps. The fact that slowpoke never got around to making the challenge maps with them, might give an indication of the fact that they do also serve other purposes.