Kaal (ESO dragon DLC) managed to absorb incredible power, consisting primarily a dozen fellow dragons sealed within the Jode's Core as well as a lesser amount of lunar energy, before he was banished.
It’s worth noting that the Vestige can defeat Barbas, who has stolen most of Vivec’s power, and Sotha Sil’s shadow, which contains the majority of Sotha Sil’s power. This suggests the Vestige’s power is comparable to that of a the tribunal. However, the Vestige is unable to counteract the life energy of a dozen dragons in Jode’s Core, even though it’s only a fraction of the total dozen dragon's energy.
We can find that the life essence available to TLDB easily outweighs all of the above cases, even surpasses Kaalgrontiid’s actions. Scholar Yvara notes that Skyrim has more dragons than Elsweyr, with many buried underground. Solitude alone has three unrecorded tombs, suggesting hundreds of dragons, possibly over 500 based on map density.
So he has an incredible amount of energy far beyond that of Jode's Core (Which only had a dozen dragons or so), To see straight through and access the knowledge of the Black Book; and even Vestige, the Destined One, can be harmed by being exposed to the forbidden knowledge of the Black Book.
Then on top of that the entire Dragonborn DLC, with you growing so strong in power that ur soul/life force is enough that it can allow miraak to escape and Mora needs you to go into his own realm, his seat of power so that u can defeat Miraak for him, and then only makes and appearance and attacks when we have already beaten his ass, only for us to them absorb the full power of miraak on top of our own.