That is so.
I have tried the turtle with Warrior on impossible. It can easily be won without losses even without healing. All it takes is to work carefully and plan carefully.
I used this lineup:
Demonologists
Archmagi
Druids
Assassins (put near one of the legs and hack away)
Beholders
These generally can withstand the initial turtle attack, unless it hits very powerful. If they do, then you surely won without a loss. Put the Druids in the middle, so that the bears they summon get to the turtle quickly and shield them.
Now all you need to do is keep 2 bear stacks up (one tanks, one walks around it, so that it doesn't fall asleep and subs when the main tank dies). I am worried that multiple stacks may provoke the turtle to do the mass attack - so take it slowly and the win is in the bag.
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