Reference

[Bbetanzos]

"more catholic than the pope", how do you express without the catholic reference

[5jj]

As the expression is normally used of someone who is a very committed Roman Catholic, it is hard to see how we can leave out the catholic reference.

[Tdol]

You could change Catholic and Pope to something different if it were relevant. You could use Manchester United and Alex Ferguson as a pairing for a fanatical Man Utd supporter, for instance, but if you take the Catholicism out of the original sentence, there's nothing left.