I suspect it depends on age and class.
My 5 year old struggled and needed a whole bunch of support.
my 8 year old was able to work on her own, but still didn't get anywhere near as good learning outcome as being in class.
Now, the reason why my kids didn't fail utterly, was because my wife wasn't working and could, just about support their learning. Until it sapped her will to live.
This is roughly analogous to junior employees. They need special attention, and providing that over remote is a challenge to scale. Not impossible, but a challenge.
You also need to factor in that Junior employees are more likely to have shit accommodation.