As you said Nellie, the Oath taken by Henry VIII is very different from that taken by more recent monarchs. Congratulations on finding this, and for sharing it with us.
In my humble opinion, the major difference is that Henry VIII did not take an Oath regarding the Church of England as an established church -- it did not then exist -- and so Henry's oath refers to the Catholic Church.
Despite the arcane language, the rest of his oath appears similar to that of monarchs following him: for example -- there is an oath to uphold the customary laws of the kingdom etc.--