I think they are trying their best to make the game good, but Arena, right now, is totally unplayable and, as you pointed out, this way to use mysteries make it even worse for people that don't have enough initiative to get a winning streak over jonin rank (i'm one of these and i'm running a meta team. Currently top 30-40 in my spacetime bracket, still at 26 -4 in arena since my server went in the cross server realm three months ago. I got more or less 5000 more initiative than i used to have at that moment, but for ranked arena seems like i got 0 because i continue to win as much as i lose exactly like before).
They could say you can abuse of that thing too but this doesn't change the fact that initiative is so much important there that is actually the only thing that matters if, like my friend Eplox showed there, you have basically no way to counter an enemy action if they correctly time the use of their mysteries (and most of my losses there are dued to this + lower initiative).
Anyways i don't think the reply Tobei gave to me is so bad as you thought, I still have a bit of faith.