Rotorspeed, such things are set by the certification rules. Manufacturers have to demonstrate emergency evacuation with the specified seating configuration. So it already happens as you suggest.
But aren't jumping the gun a bit? We don't yet know why some of the pax didn't escape. Maybe they were knocked out or otherwise injured in the impact? Maybe they panicked and took a large lungful of water as soon as they were submerged? Maybe they froze in panic?
It is one thing to know that they didn't get out, but it is a non-sequeter to conclude from that, that having a more spacious cabin layout would fix the problem.