The very scriptural nature of Catholic worship
It strikes me, that had I been better equipped I could have swatted away their arguments like so many bothersome flies. Think about it. When properly celebrated (i.e. using the texts rather than the four-hymn pattern that is usual at Sunday Mass) Holy Mass, (EF or OF) consists of the following:
Introit antiphon (Biblical text)
Kyrie (Derived from phrases in the gospels)
Gloria (A hymn of praise based on the hymn of the angels at Christmas)
Liturgy of the Word (OT, NT and psalms)
Creed (formula based on the bible)
Offertory antiphon (Biblical text)
Sanctus (derived in large part from OT & NT)
Eucharist prayer/Roman Canon(a long prayer of ancient proveneance with Christ's words at the Last Supper at its core, full of allusion to the bible)
Communion Antiphon (Biblical text)
How biblical do they want it to be?
My Baptist former colleague just came back from a holiday in the West Indies. She attended a Protestant service there that lasted 3 and a half hours - most of which was preaching by the pastor. Now, compare that with a Low Mass where the worship is of Almighty God - directed solely at Him, and composed largely of words from the bible. Which then is biblical Christianity? Which then is more reliant on a mediator between God and man - the one where a chap barks at his audience for hours on end or where God's own words are addressed to him by a priest on behalf of his people after the biblical pattern of worship in the Temple by a priest secundum ordinem Melchisedech.