What makes you think Galatians 2:20 does not apply to Catholics?
It wasn't my opinion; it was yours.
You said "the Catholic Christian receives the Living Christ every time he comes to Mass."
Therefore since the Roman Catholic supposedly receives Christ during the Roman Catholic mass, there must be times when Christ is absent from the Roman Catholic (assuming the Roman Catholic is not attending mass taking the Lord's Supper 24 hours a day.)
This opinion of yours is unlike the assurance experienced by Bible-believing Christians who know and believe Gal. 2:20 which says Jesus Christ indwells His sheep 24/7. Christ is never absent from His sheep.
Therefore it's you who has excluded Roman Catholics from Galatians 2:20.