Yet the "alone" also meant, particularly at the time it was first used, all those three (grace, faith, scripture, along with the other SOLAS) with the pointed exclusion of:
As it was, and still is to a variable extent, we find this group seeks to interpose themselves between the seeker of Grace, and the actual giver of Grace. Fall out of favor with this group, and the threat is one shall in all ways be cut off from the Graces or favor of Father/Son/Spirit in entirety.
It was in the light of this sort of posturing, that the "alone" usage was employed. As such, it brings clarification that one need not be an actual member of this one religious group to have hope of salvation through Christ.
I would give the full and official name of this group, but if I did so here on this forum, I'd be accused of being a "hater"...
I think I know the name of the group that you mean—but in my experience, far from trying to interpose themselves between the seeker of grace and the giver of grace, they plead practically non-stop both with God (when they pray “give us this day our daily bread) and with every seeker of grace who will listen to have the seekers of grace have the giver of grace crammed (not the right verb) down their throats every day. Far from interposing between the seeker of grace and the source of grace, the priest takes away He whom we have seen with our eyes and he whom the priest has held within his hands and leaves him on my tongue.
As for the use of the word alone, most heresy comes from neglecting some truths while exaggerating others. Christ is God and man. He is not God alone, he is not man alone. The use of the word alone is a good clue that the theology is flawed.
This is the key point... authority. You follow Grace alone, Faith alone and Bible alone. In that, you must trust to private revelation and interpretation which has been decried numerous times on this thread. These private views of spiritual matters have brought disunity in Christianity where Christ prayed for us to be one as He and the Father are One.
So we come back to the issue of authority. Scripture records who was given authority... and it was before we had the Book of Romans to memorize. It was the Apostles (Matt 16:19) and their successors (Acts 1:20). This is the whole reason that there are Epistles... they were written by Church men of authority to correct errors in the targeted churches. Without Church authority, there is no New Testament Canon... and no Church!