After the episode "Mr. Greg" and from the recent clip from the CN App, I believe that Steven's abilities of Healing are stronger than Rose's and that this has been present from very early on in the series.
From early on Steven has shown an innate ability to help people, and empathise with people. He seems to be able to support people both mentally and physically. Examples of this are; "Indirect Kiss" "Rose's Scabbard" "Ocean Gem" "Gem Drill" and "Mr.Greg". All of these episodes show Stevens ability to essentially help or heal someone both indirectly to help someone mentally and directly help someone physically.
Well with evidence from the CN App In the Clip from the CN App Steven is able to heal a corrupted Gem, which suggest his ability to now directly heal physical and mental damages.
Ontop of all this I would like to suggest the prospect that Rose's Powers didn't come from her emotions unlike Stevens, as Rose was trained as a Homeworld Quartz Soldier, and that this tie to emotions is what allows Steven to heal people and gems physically and mentally through his healing spit.
This seems like a pointless theory but what do you people think could this be accurate?