Lets be honest after clearing the fight 20 times, chances are you're already good at it. Any more than that is just brainless repetitive task, its not even fun anymore. I dont like it personally. My suggestion is to make it so that if the mount drop (still a low chance), every player that clicks the chest automatically gets it in their inventory, it works the same as books in savage raids.

That way the content will actually become more fun for everyone. No more salt for losing rolls and the drop chance is still low enough that you have to do it multiple times. But it wont be so bad as collecting 99 totems and once it drops everybody is happy.