I myself agree that Black Mage's down smash is currently really bad by itself, it's just a slower and much, much weaker up-smash that covers the ground
...Except that it's too slow to let you punish the opponent while they're frozen, also they barely even get to land on the ground before thawing, and if mashing quickly enough, they can get out before even reaching the peak of the knockback's trajectory

What i mostly want for his down smash is for the freeze time to scale with damage up to a certain point (maybe as long as a charge-4 Stop at max, while full-DSmash freezes for as long as charge-5 Stop, but mashing will actually help escaping)
I did notice in the streams that his normal DSmash's knockback angle has changed somewhat, but nothing visibly changed for full-DSmash (though everything is still subject to change)

Also, when frozen, attacks deal no knockback; making it not that good. Especially when you need kill confirms as Mage. USmash and FSmash are just way better and more versatile then down smash

I've gotten plenty of kills from Goku and Luffy's Dsmash. In fact, both their Dsmashes feel more powerful than their Fsmashes when uncharged.