Welcome aboard!People have been wrongly trained for centuries by the Romans and Roman Catholicism, to see things in this world upside down and backwards. And that includes when the day actually begins and ends.
And just to nitpick, it's a tad unfair on Roman Catholicism as the Friday - Sunday tradition was a practice across the entire Church, before the Roman Catholic Church existed as a distinct entity. In fact the majority contribution to the discussions was from the Greek East, and thus the Orthodox Patriarchates likewise observe the three days.
And again, Catholic exegetes have evidenced the materials you offer above for quite some time...