God bless you for your spirit of inquiry.
A fair minded protestant doesn’t have to agree with us, but as you can plainly see, it takes an intellectually dishonest one to claim our doctrines have no biblical merit.
When threads like this one get heated, some people, Catholic or protestant, retreat into the trenches of absolute statements. Then it becomes a to-the-death battle to maintain a position that is logically and rationally indefensible.
Or they attack the person or intellect of their partner in the discussion.
Not my cup of tea.