Although Santa Claus is technically a Demi-Archangel he still isn’t the strongest person on Earth. In fact, his evil twin brother, the Demi-Archdemon Anti-Claus, is nearly equal in strength. You would think an Angelic entity would be stronger than a demonic. However since they are identical twins they have a symbiotic connection. When Santa’s abilities skyrocketed to Archangel powers upon his Christmas resurrection several centuries ago, the Anti-Claus got the same increase in power! Unfortunately this only works for base powers. So if one harms or weakens the other there isn’t a similar reaction in the other. If that was the case the Anti-Claus would never dare attack Santa for fear of a mutually assured destruction.
Santa Claus is most likely the strongest natural born biological being on Earth. However if various supernatural entities such as Angels, Demons, Jinn, Earthly Gods, and others of higher dimensional origin took a physical form they would be more powerful than the Great Claus. Of course the Spirit Of Christmas affords him magical powers beyond physical strength. For security purposes Santa doesn’t want to make his full power known but we’re pretty sure he could hold his own with any number of paranormal titans! Santa Claus is considered the leader of good on Earth with Christmas being the central holiday that counteracts paranormal evil. So his stupendous strength is good for morale when it comes to those fighting the forces of darkness!