With customs, I think either +1 or +2 for WFT.
I think this MU rides entirely on the one, single move that overhauls WFT: The Jumbo Hoops
WFT literally turns a whole new leaf with the Jumbo Hoop, which lets WFT kill off Luma at any time, and there isn't much Rosa can do about it.
If Rosa gets caught in the move, whether she blocks it or gets hit by it, Luma's basically guaranteed to be gone.
WFT is vulnerable when landing after the UpB, but she can end it over an edge to grab it, and reset the situation, meaning Rosa isn't guaranteed a punish even if she does manage to outlast the Jumbo Hoop without taking damage.
The only reprieve for Rosa is that she can stop the UpB either by poking at WFT with Shooting Star Bits, or preempting the UpB with a Floaty Star Bit, walling WFT out if only temporarily.
Rosa's only means of avoiding it are being below WFT (which is sometimes not feasible if WFT does it on stage or if there isn't a edge close enough), being above WFT (also not feasible sometimes, since WFT can mash the UpB to rise into you), or with a projectile...which Rosa only has when Luma's around, much less not tumbling.
Custom WFT has a lot of tools to either dispose of Luma or disregard Luma, as she also gains Enriched Salutation and Sweeping Salutation.
Enriched charges and travels quite fast, while being undeniably strong: If it hits Luma, it'll likely tumble it into the blast line.
Sweeping is a piercing projectile, which does not bode well for not only Luma, but Shooting Star Bits as well.
If Rosa takes the time to Pull either one, WFT can simply get the Jumbo Hoops off the ground while Rosa does so.
If Rosa is caught offstage, WFT can set up a literally impassable edgeguard by hanging off the edge, dropping, and putting Jumbo Hoops out there, blocking Rosa's path to the stage if she can't recover high.
The amount of control WFT has over the placement and duration of the Jumbo Hoops with an edge nearby to cancel it with essentially puts up a test of how long the Rosa can tech stage spikes if, again, she can't recover high or otherwise recover around WFT.
On the other hand, if WFT is offstage, Rosa can poke at WFT exposed head with DAir.
If Rosa gets the spike, WFT can't do much since Jumbo Hoops have lesser vertical travel distance--even with maximized mashing.
On top of all that, Luma has a noticeably hard time hitting away any and all of WFT's soccer balls without getting hit as well.
Again, if Rosa takes the time to Pull, WFT can use the opening, where Rosa is guaranteed to be unable to put out a projectile, to get Jumbo Hoops out, sweep the screen, and likely clearing Luma as well.
Rosa will inevitably have to become very familiar to fighting without Luma, as he's guaranteed to be taken out very quickly if he isn't constantly out of the picture.
This MU can be incredibly frustrating for Rosa.