Handull it becomes a matter of mathematics with a manastone for encounters like this.
First you have donals BP wrong - right now its a 20 second cast time, mana free CH that can be recast immediately.
Second the true power of the manastone is in its mana to hp conversion ratio compared to the mana to hp healed ratio of the healing spell being utilized by its user. Lets look at a cleric as you're using in your example. For simplicity sake in math lets say he has 3000 hp self buffed.
With a mana stone you exchange hp for mana at a 3 to 1 ratio. With our above mentioned cleric they could conceivable exchance 3000 hp for 1000 mana (I'd assume they regen an HP or 2 by the time they're done clicking their stone 50 times).
After a CH, spending 400 mana, thats a net gain of 600 mana. Pretty good for about 12-13 seconds of work in the old world.
The true problem with this scenario is that Ragefire AoEs.
Thus a cleric cannot mana stone down to 1% before CHing. They would conceivable have to stone down to 40% or so and then CH to prevent AOE or if the tank takes a fear and they're at 10%...they have to leave a buffer incase of an unlucky aoe. That means they only have 1800 or so (60% of 3000 hp) to stone down. This yields them 600 mana; after a CH thats net mana gain of only 200 mana.
200 mana instead of 600 mana gain is huge. It means they have to stone down twice and CH twice to be able to regain the mana burned from 1 CH on their tank. Thats 22 seconds worth of work (if you're spot on timing stoning down/ch 22 would likely be the bare minimum) to be able to regain the mana to cast 1 spell that takes 10 seconds.
Total time = 32 seconds per CH compared to 20 seconds on Donals BP CH. More like 34-35 seconds with stoning/CHing.
I don't think it can be done tbh. Perhaps I'm playing it safe saying only to stone down to 40%; Maybe 20% of the clerics hp would be safe. If so that would be a net gain of around 400 mana per stone and thus a CH recast time of 22-23 seconds on the tank.
Someone please prove me wrong
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