It would be much better if Camera Raw had a feather effect tool in the masking section. Because after masking, a thin, white line appears around the object that looks awful.

It depends on what mask you use. some work better than other, for example, Landscape>foliage, always goes too far into the sky and has to be edited with a subtracted mask, such as the brush tool. That said, it would be nice to have a feather option on many of the masks.