I don't think it would help at all people are usual sick of the fights if they have to go 99 kills especially if anything annoys them about the fight and adding a 1% drop rate mount would exasperate the problem especially down the line as newer players join, I got my nightmare pony during HW when i was tank mount farming, not going for it properly.

However if they was a way to mitigate the rng say with needing 30 of every trial of the expansion totems etc then i would be fine with an absurdly low drop rate. One thing i have learned if your going to have rng there needs to be a way of mitigating it so you are always progressing(working) towards your reward, this is why Blu primal skills are so hated, why ponies had to be buffed signifacantly even compared to buffed lanners/doggos.