Several NPCs in Skyrim (Esbern, Parth, etc) allude to the notion that Alduin is supposed to eat/destroy the current kalpa so that the next one may take its place, but the game failed to give any indication that Alduin could do this nor did Alduin himself ever state that ending the current reality was his ultimate objective. If his purpose is to end the current world, what was he doing back in the Merethic era ruling as a dragon overlord? If such is his power that he can devour existence, how did some puny Nord tongues manage to trick-f%ck him into getting sent to the future?

I'm not really disputing the idea that Alduin's ultimate destiny is to end the current kalpa, just the game gives no indication as to what goes into that, or that we are even preventing reality's imminent demise at the maw of Akatosh's "first born." Instead it casts him as a dragon overlord who wishes to regain his lost dominion, not some world-ending mythic force. So is this simply an error on Beth's part to not adequately show his capacity for "world-eating" or is there something I'm missing or something I haven't come across which would explain the gap between the Alduin which is supposed to end the world and the one we fight in Sovngarde?

Also I'm aware of the conjecture that Alduin may actually be Akatosh or an aspect of him, and is simply confused as to his own identity and thus severely limiting his own power through this delusion. Is there any text to support that though, from MK or other sources?