Just for my own curiousity and some testing , have you tried the dynamic brush tool.
This thing; 
And giving your opinion on how it compares to lazy nezumi style smoothing, this brush tool is closer to sai smoothing as far as i know. Im campaigning for its move as a smoothing option under under brush. 
Yes to the softness - I’ve very little experience with other software but i do want softer brushes that i can control the softness level. OTH they do really have very different brush engine but i do want more softer brush myself.
Yes I think this would be beneficial, would you mind paying visit to this thread. If there is anything you would want to add there.