I personally feel that it would work a lot better as an e ability, rather than an ultimate. Either way, I agree. It’s been a serious downgrade indeed. 
At that point I would rather prefer Mercy to have res charges, that are earned through her healing / damage boost, which are then used exclusively in Valkyrie. Nonetheless, that would certainly be an upgrade over what she has now. 
~Sincerely Yours xoxo,
a Lover of True, Fair, and Fun Balance.
xavvypls 