It doesn't surprise me at all that selectable clutches are not being used in modern designs. I have known of several cases of pilots making the wrong selections and shock loading the gearboxes. In some cases it was a matter of them having learned the routine without learning why it was required. In others it was simply a case of loss of concentration. But the result was pretty much the same in all cases.
Getting back to the assertion that all helicopters require clutches. This is not true.
And getting back to the original question of what is the main advantage of free power trubines. It is as I described.