"...they were not buildings whose sole purpose was prayer/liturgical celebration which is what the word "church" (in its architectural meaning) usually designates."

Again, making a claim of certain knowledge that you cannot possibly have. You claim to know that these buildings, 1700, 1800 or so years ago, did not have the "sole purpose" of prayer. Really? How can you know this?

Even if the buildings originally were homes, you know -- in AD 2017 -- that they weren't subsequently converted entirely to worship?

And, in any case, the fact that these buildings are, indeed, widely called "churches" -- not by me, but by a flood of citations on the web -- disproves your claim that they aren't properly termed churches. Who made you the decider of what the word "church" means?