It seems to me the Dovahkiin really wasn't needed at all in the events of Skyrim.

Early on they made this big song and dance about the fact the Dovakiin could absorb the souls of dragons and destroy them permanently. Also we know the Dovahkiin's thu'um was stronger than that of Alduin himself, but that ultimately is irrelevant.

The final battle takes place in Sovengard - and yes, the Dovahkiin forced Alduin into Sovengarde to recover; but Alduin would've returned to Sovengarde sooner or later anyway so this is irrelevant. Dovahkiin rallies the 3 heroes; but they could've easily rallied themselves if needed - The fog required the concerted thu'um of 4 tongues to clear, but there's more than just 3 versed in the thu'um who exist in Sovengarde amongst the ancient nords, they could've brought reinforcements if the 3 alone were insufficient (Dovahkiin's thu'um might be strong, but an army of ancient nords with basic knowledge of the thu'um could do just as well).

In the battle itself, Dovahkiin's input will vary but ultimately the heroes alone can defeat Alduin without any help at all (In my playthrough I was useless being reliant on shadow warrior for most my DPS, and the 3 dopes were holding agro on it), while in-game they're too lazy to use dragonrend and rely on Dovahkiin for this, we do know that these 3 heroes know the words; they invented them afterall. So they don't need Dovahkiin for the dragonrend either.

Finally, when Alduin is defeatted, his soul escapes, Dovahkiin isn't able to absorb it, so the Dovahkiin's McGuffin doesn't work on the one dragon who people really want dead.





So, what's the logic behind making such a big deal of the Dovahkiin, other than being the prophecised figure who puts it all into motion? - His knowledge of the Thu'um and his ability to absorb souls is ultimately irrelevant in the grand scheme of events