Did you forgot to add the image? 
I also tried with an already made
landscape, specifically the Spring
Landscape free this month. I
experienced the same results.
Yes it won’t make any difference, since it is how the sculpt tool is working that causes the sharp edges.
And I set the strength of the smooth tool to something very low, so around 0,0001 - 0.0003
But yeah, this might be a pain to get correct, so to smooth it but not change the landscape.
But the problem is that I don’t use the sculpt tool right now, and I don’t know when I might need it again, so I can’t really help you there.
Basically what might help you
(1) When you sculpt, use a greater falloff and don’t use too small brush sizes
(2) Maybe look into landmass and blueprint brushes and try using those instead of sculpting for most of the time