Also in regards to Alduin, there is the argument to be made that his "World Eater" form does not scale to the Alduin you fight in Skyrim (Which I always disagreed but then ESO added this):
"Alkhan. The Scaled Prince. Firstborn of Akha, who bred with a demon of fire and shadow. He can devour the souls of those he kills to grow to an immense size. The songs tell us Alkhan was slain by Lorkhaj and his companions, but as an immortal Son of Akha he will return from the Many Paths in time. He is the enemy of Alkosh, Khenarthi, and Lorkhaj, and ever hungers for his crown."
"He can devour the souls of those he kills to grow to an immense size". So why does this matter? Well, it's because we see it in the Seven Fights of the Aldudagga:
This text was originally posted on the official Bethesda forums on November 19th, 2005.
www.imperial-library.info
In the Aldudagga, Alduin is described as this colossal beast that can devour nations whole, whose shadows are draped over all four cardinal directions, with nostrils so big that whole farms can fit inside it. And this is Alduin in his World Eater state. The Aldudagga also says that Alduin "always eats the Nords first", implying that his devouring starts at a smaller scale and eventually he eats the entire world.
Obviously the Aldudagga is a Silly Folktale that I don't think is meant to be taken literally, but it is informative on the nature of Alduin. And what's more, it and the ESO bit do corroborate with Skyrim itself, where Alduin flies to Sovngarde to gorge himself on the souls of the dead to increase his power.
Skyrim also states that Alduin abandoned his role as World-Eater to rule over the Mortal World instead, so he's not even trying to initiate the process of ending the Kalpa and would, therefore, theoretically not possess his "World-Eater Power" at that point.
And then you also factor in Dragonrend and you can easily make the argument that the Dovahkiin doesn't scale to Alduin very much at all - At least as far as the base game goes, because as of the Dragonborn DLC he scales to Miraak who is directly attested to being more powerful than Alduin, and to being able to easily kill Alduin on his own despite not knowing Dragonrend.