They have always sold seats directly to the public
That statement is untrue. The facility to make direct bookings with Viking via its website has only (very) recently been introduced.
The point I was making about ATOL cover was that up to now, anyone buying seats on these flights would have been covered by an ATOL. Now they are not. I agree with you that it simply places Viking on the same footing as the likes of Ryanair, but I think the diference is that Ryanair didn't leave a trail of destruction in its wake to get to that position in the first place.