If you're in a supporting role, you should have Haste Samba up. In other words, waltz recast tied to Fan Dance is more or less completely worthless.
Fan Dance is hardly EVER used in support situations (exception being oshit moments), I'm not suggesting this.
I entirely forgot about those pants being merit based. Thanks for correcting me.
As far as the merits go, the new update does more for a soloing Dancer than one in a supporting role (excluding pants altogether).
The additional couple of seconds of attacking is nice of course, it's just that
when you're in a situation where you need Fan Dance, the waltz recast helps you a lot more.
But I agree, 5/5 Saber Dance is still the way to go.
Edit: I don't think I put it the right way:
Essentially, the waltz recast bonus is a better update for Fan Dance than the samba duration for Saber Dance, it's just that most likely you're using Saber Dance so Fan Dance is still not worth meriting.