I think the biggest difference between Mormonism and Catholicism seems to be that Catholicism and Mormonism both teach that you can reach perfection, but Mormons hold this equivalent to god-hood. Catholics, on the other hand, consider the singular essence of the Father, Son, and Spirit to be the only form of God-hood.
Regardless of any amount of perfection, no other being can ever reach this state, simply because their essence, even if derived from this same essence, has taken on a form of its own and exists separately from that essence. An argument would be made that Jesus’ essence was separate from the Father’s, rendering him perfect but not God by this standard. The obvious difference is, of course, that has been ancient Christian believe that Jesus was simply another facet of the same God, begotten, not made.
The Bible states that “All things were made by him,” in reference to the Jesus (the Word). Of course, by my understanding, both Catholics and Mormons affirm that God the Father created all things. If Jesus also did, it bears to reason that Jesus IS the same God as God the Father.
We could try, of course, to complicate things with arbitrary definitions of union and existence which allow for perfect unity between Jesus and the Father, allowing them to act as one, and yet they still be separate. It’s been tried before - only a couple hundred years after Jesus. It’s called Arianism, and it was deemed heresy.
Just a thought.
P.S. - Regarding the constant stabs at Mormons for their “blood sacrifices” - let Catholics not forget our heritage of flagellation and the shedding of the blood of others. Catholics have also been persecuted, of course, but we also did a fair share of the persecution. If you would judge the Mormons by this standard, then expect to be judged by the same.