I did most of the changes to the shadow dragon you suggested. and gave the breath a smaller AoE, and reduced his precision.
I took the hunt off the draco sanguinius (but not ars sanguine) and increased his path cost to 85.
I toned down the madness strike so it isn't as accurate as it was before. Its already low damage low ammo.
Your suggestions to gold dragon completely remove what I added for thematic purposes. Dragons breath things, I'm not going to just make him a mage with an auto flamestrike (circa MoM) If you want him to cast magma, then give him a level of fire
He breathes magma, he doesn't have to cast it. I'll reduce his fear by three, and up his cost.
I'll reduce the storm dragons hp to 90.
keep in mind dragons, even in CB, can solo indes really well too, so the fact that these dragons can should be no suprise.