I don’t think he’s only just realised what RLC brings, I think RLC hasn’t been capable of playing regular games because of his fitness issues. He’s even mentioned that himself.
Emerson and Alonso are as hit and miss as each other IMHO, I think it’s pure luck whether you get either of them on one of their good days.
As for CHO, as mentioned elsewhere I credit Sarri for helping his development in the first place as much as I do for criticising him for not playing him more. I wonder if the Bayern flirting hadn’t have happened, whether he’d have played him more, earlier.