This MU changes significantly based on customs or not , skill levels from low -> top and the overall play style of the players.
Default 50-50
Customs 45-55 for Rosa or 40/35-60/65 for Rosa
So from a zss main PoV I will agree that Rosa has the edge depending on stage in all skills levels if customs are on not because of the warp star , More along the lines of the quite literally eff you single star side b shot. Even on stages like bf or something where we're not confined to the ground I literally want to rip my hair out sometimes when I get hit every other second by a single star. I feel extremely comfortable in this mu(normals) even to the point of being fine with fd the stage I hate most. To me this mu isn't patience it's knowing
how to and when quickly finish luma , using luma to refresh moves and a test of your ability to burst rosalina and unload as much % on her as possible in the short window after a luma death.
Those johns aside in terms of normal mechanics I disagree that Rosa beats zss hands down like alot of people say
GRANTED I HAVE YET TO FACE A ROSA OF DEBUZZ'S CALIBER.
Knowing myself personally I honestly have to say that I am more than likely near the top of mid level bordering into high level in a competetive sense. ZSS has alot more anti luma tools at her disposal compared to a majority of the cast and some of them are exceptionally potent for the luma MU.
Some of those include the use of zair (if you hit Luma while she attacks it will halt that action and proceed to hit Rosa if she's not shielding (gotten away with zair approaches or retreats simply because luma has to wait 1 frame after Rosas input).
Another tool is side b which while looks like a terrible move it literally chains into itself on Luma due to her knockback resistance , Also hits when Rosa is shielding (I am totally fine with a grab, upsmash or dash attack punish if it means making the Mu easier for the duration of the respawn timer).
Last is the stuns via laser and down smash, now laser can be used to stun luma during any luma shot except for a fully charged one I tend to go for full shots but uncharged ones work just as well. In regards to the downsmash this is where luma's taking low knockback trait which is usual a strength works against it, if you downsmash luma at the edge of the hitbox she will take the lighter knockback from it. This literally causes luma to just get stunned and not move a muscle which you can infinite her until Rosa interferes which can also be used to refresh your moveset.
Edge guarding rosa is easier then most people make it seem because of Zss's dair which can just deny you from recovering whenever the zss has complete control of the timing required ,and if she doesnt there is the edge trump set up to just do it if she regrabs while if she doesn't flip jump kicks or dash -> boost kick or grab combos are free.
if all else fails just run of jump and bair stage spike -> pray she doesn't tech and move on with life.
People get impatient with the fact they take % from luma and Rosa is "camping/being defensive" until your at kill %. I believe this is a misconception she's not camping you Rosa is a puppet character doing what puppet characters do. I always treat her like a boss encounter generally following these 2 rules.
1. If Luma is up do not bother with Rosa because you can not always adjust to the random eff you power hits from luma. When luma's dead dps Rosa until respawn and if you have the presence of mind snipe luma upon respawn which things like side b dash attack and others will deal with her-> rinse and repeat.
2. When ever you grab Rosa and throw her (do it right away btw) always shield immediately because luma is more than likely going to knock you on your *** for your transgressions against the master.
Things to consider in terms of stages which you guys probably already abuse is, the fact that zss is good at platforms but ok most stages with platforms especially zss's best ones like bf. Rosa literally murders you for ever landing on a platform. I'd recommend stages like
bf and LyLat even castle siege for the small space while giving you extended luma Hitboxes on the statue phase.it kind of sucks for a ban but getting rid of omega might be a good idea because it gives zss the option to tether cancel and wall jump Shinanegans to avoid your dair.
sorry for the novel work from 3am and anything else I say is a huge John.