It was not a good idea because now there is even less of a reason to worry about how ones team is able to defend its position. The developers needed to either keep it blind or give defending teams support.
That said, I already know who all my opponents have and can guess their squad composition pretty well. I use the same 5 characters every battle (only have 5×7*s) so i am quite sure this has zero effecton me, since whoever is attacking me is almost certainly not doing jt for the 1st time (i finizh 1-6).
So, while i like browsing my opponents characters, and while this really does not effect my Arena experience, I think keeping it blind was the better option, especially since defending was well nigh impossible in the 1st place.