Edit: I meant to place this in Reply the 1st time and not start a new block. D'oh!

This dose not really address the main thrust of your point but in vanilla it was pretty obvious that the Black dragonflight (and what was left of the old Orcish horde from Warcraft II) opposed and fought with the dark irons and servants of Ragnaros.

This leads me to believe that the old gods/ twilight's hammer alliance with Deathwing and his dragons is a recent affair. Also I was under the assumption that Deathwing and the Old gods were more using each other for short term gain as opposed to having a faithful master servent relationship. Just because they corrupted Deathwing dose not mean they can control him.

Also In Blackrock depths it is pretty clear that Thaurissian and had the help of least 7 other powerful dwarven mages of 1 stripe or another helped him summon ragnaros so its not like he did it alone.

None of this means that Deathwing or someone else didn't plant the ideas in their head, or give them pointers on the summoning ritual. Though sometimes you can benefit immensely from some one the actions of some one else, without starting some massive conspiracy to get them to act that way. Sometimes you jut luck out.