I'd say it's a matter of opinion as to whether there's only on reasonable approach to Silverthrone. One can take abush plane from Talkeetna into the Don Sheldon Ampitheater (or possibly even higher up) and do the peak with considerably less effort than the route you describe. Might even leave you with a week or two to undertake other ascents in the area.
The South ridge from the Don Sheldon ampitheater used to provide an easy way up, but with the break-up of the main icefall in the North Fork of the Ruth Glacier, it is no longer an easy or recommended route.