I would counter that by stating that the B767 first flight was 1981. A320 was 1987. B777 was 1994. B777 is a much newer design than B767 using composites. B767 is an old style aluminium plane - (which is one reason why Boeing chose it for KC-46). Not difficult to believe a B767 and B777 will break up in different ways.
Hopefully a B777 will behave much more like an A320 than a B767 in a crash. The only way to find out for sure if it's possible to land a B777 on water without it breaking up is to try it. No-one is going to do that - even remote controlled.
Yes the miracle on the Hudson was on flat water. The area where MAS370 is believed to have gone down also had relatively benign weather that day. However, since we don't know exactly where that was it's impossible to know the sea state with any accuracy.
Landing speed of a B777 is 135kts/155MPH. Landing speed for an A320 is 140-150kts. Providing there is a pilot in control, and he configures the plane for a wheels up landing, there is no reason to think speed would be very much different.
Altitude is irrelavent as long as there is a pilot in control. The plane may well glide like a brick, but the hydraulics still work with both engines switched off, so the pilot can control the descent and choose where to land (crash!). Deadstick landings have been completed many times -
https://en.wikipedia.org/wiki/Gimli_GliderMost of the damage on the BA B777 was caused by the wheels ripping through the wings and fusealge. If the wheels weren't down that would not have happened (not suggesting they shouldn't have lowered the gear). The fuselage was basically intact - barring the damage from the wheels. If that had happened on water, almost all the airframe would sink to the bottom. Only the lighter than water parts that did break off would be found.
AIUI the Air France aircraft was 'flying' in a roughly 45 degrees nose up attitude, all the way from FL370 down to (almost) FL000. A fighter jet has enough engine power to maintain altitude in this attitude. An airliner doesn't. The flight control computer stopped the aircraft stalling, but the pilot was trying to pull the nose 'up' almost all the way to impact.
Anyway - need to go to bed - gotta get up early tomorrow to go see 12 F-22A's :-)