But it makes sense from a logistical standpoint. You entered as a team, so you should be able to finish as a team. If you needed only one person to keep things going and pass content, is that not called "solo play?"

Then the current concern should be to make content soloable.

That is no different than entering a random battle with 4 party members, but three of which are already dead. Your point in referencing the old FF games is moot here.