The ending was a mind--blam!-, but a necessary one in order fix the franchise's deteriorating lore.
Technically though, we are Big Boss. The ending made that quite clear.
English
-
The boss we played as basically did -blam!- all and left, so -blam!- that guy. Medic then goes on to die in MG1. Again taking one for the team when it should have been Boss.
-
Which is why Kaz is pissed at Big Boss and ends up working with Liquid.