D.va buffs were necessary. She was essentially Winston lite before the buffs.
Were the buffs too much? Perhaps, the ult timer could probably do with being notched up half a second, but I wholeheartedly support the change to defense matrix, it now allows D.va to pick how long she blocks without punishing her as hard.
Is she now broken tier? I doubt it, she still loses to Reaper and struggles against Pharah, and she doesn't bring anything significantly game changing to the field with her buffs, since most of them were quality of life changes.