To be fair, Force Healing has been part of canon in the EU (and let's not pretend Disney didn't just pluck things from the EU for the new movies anyway) and the only reason they put out episode 7 of The Mandalorian the day before Episode 9 came out was because Force Healing also plays a factor in that episode. 

The Rise of Skywalker is bad but it's bad because JJ Abrams' entire thing is that he likes introducing story ideas but doesn't know how to end them, which is why Episode 9's ending is so hollow and ultimately does a disservice to the characters across the board. It doesn't help that the movie feels so 'written by committee' in a terrible attempt to please everybody rather than letting a director have a voice and vision for the story...which they had with episode 8 like it or not. 

Personally the 'canon' of Star Wars is a weird thing to get hung up on because the canon and abilities of Star Wars are constantly changed and enhanced anyway that it becomes people unwilling to accept one thing because it 'breaks canon' despite it just being the same thing the other movies did: introducing new Force Powers or techniques. Star Wars canon had tiers of what was and wasn't 'true' canon so really, Star Wars canon was fucked and the slavish devotion to it having to be one way or no way is pointlessly limited. 'Why can a Force Ghost use lightning?' Because fuck you, their creed ends with 'there is no death; there is the Force' that's why. 'Why can Luke use the Force to jump out of the carbonite chamber?' Because fuck you, that's how the Force works.