Successfull ditchings with large jets have been done before:
A B707 cargo aircraft landed 5 km short and ditched in a lake in 2000. It floated at least until the next day.
Yes, but the fact that they were empty, low on fuel, with no cargo, final approach, all engines available, was a major contributor to that successful ditching. US Air was "dead stick", heavy and at a much higher sink rate. The stressing forces applied were much higher as the plane "sunk" at the first impact.