Defending a creative process is always dangerous because it becomes a slippy slope into "I disagree."
But, let me try to give some answers, even if they are overly-simplistic.
I changed the core mechanics of the ABCs to reflect a tone of Hastur--willpower, mind control, limitation. Also, with less focus on what ABCs you can play, it should help to turn a player's attention away, toward somewhere else it needs to be to defeat Hastur: carefully controlling your ticks.
In a normal game of WoW minis, you have a lot of things to choose from: Which minis you will use, which ABCs, when to engage the enemy, how to control your ticks, how to control the enemy's ticks, how you control your movement, how you control the enemies movement, etc.
In a Raid environemnt, you are right: one can just up the volumne on the Raid Boss and give him crazy high stats/powers. One can also tweak other aspects of the game to create a unique environment--in Hastur's case: clock control. There are other models. Sadly, not everybody is going to like each model. Crystalline Devourer was an example of being ready to deal with each threat as it arises--mostly, in picking the right character/abc combinations to handle those threats. For Hastur, the characters themselves aren't super critical. Two ABCs are critical. Something to increase your movement, and something to shut down healing (a pet helps, too, for the Blight Tokens). I think your metaphor of a chess puzzle is mostly correct. Some players like that; other's can be frustrated by it.
Raid 1 and Raid 3 play very little like a chess puzzle. Each player will have their own favorite Raid.
Something else came up with another player which also bears mentioning. Beating a Raid is fun in Minis or Online--but it is fun because it is an accomplishment. If it is too easy--if it is beatable on a first try--there is little accomplisment involved. This is my personal belief, and I can see how others might disagree. As I said, "slippery-slope." :-D
With three factions to choose from and about 1/3 of the total minis being 4 or 5 honor, there are lots of choices to make. Your example of Mortal Strike is almost right, but there is at least one other option. The core of what you said is true though--if you are fighting a Raid Boss that heals significant amounts of damage, you have to bring a way to shut that down.
All in all you are right: Hastur is tough, tricky, a puzzle, unforgiving. His soul is bent around Willpower, Limitation, Mind Control.
PM if you'd like some hints if you find yourself getting repeatedly stuck. I think though, that you will find a way.
-c
http://myworld.ebay.com/corle2/