They have a "fluid" doctrine that can change with the prophet.. so it is "all good" for them
This is not true. Nobody --- no "prophet," no Pope, no Synod or Council ---- has the authority to deny or abolish doctrines which have come down to us from the Apostles. And Public Revelation ceased with the death of John.
Here's a succinct expression of what we believe:
I believe in one God,
the Father almighty,
maker of heaven and earth,
of all things visible and invisible.
I believe in one Lord Jesus Christ,
the Only Begotten Son of God,
born of the Father before all ages.
God from God, Light from Light,
true God from true God,
begotten, not made,
consubstantial with the Father;
through him all things were made.
For us men and for our salvation
he came down from heaven,
and by the Holy Spirit
was incarnate of the Virgin Mary, and became man.
For our sake he was crucified under Pontius Pilate,
he suffered death and was buried,
and rose again on the third day
in accordance with the Scriptures.
He ascended into heaven
and is seated at the right hand of the Father.
He will come again in glory
to judge the living and the dead
and his kingdom will have no end.
I believe in the Holy Spirit,
the Lord, the giver of life,
who proceeds from the Father and the Son,
who with the Father and the Son
is adored and glorified, who has spoken through the prophets.
I believe in one, holy, catholic and apostolic Church.
I confess one Baptism for the forgiveness of sins
and I look forward to the resurrection of the dead
and the life of the world to come. Amen.
This is our Credo. If you want to dispute "what Catholics believe" this would have to be your principal reference.