I think it's more a case that the first GRQ-SEN cannot connect with the first wave DUB, GLA & MAN departures so maybe they're just playing safe offering the middle of the day departures to DUB and MAN/GLA at this stage. I must admit I didn't look at the return flights and having done so I cannot quite see why only a Sunday return from DUB and MAN is bookable.
Maybe there's some more to come as you say but with respect I don't think there's anything in the suggestion made by koninckske regarding additional RNS flights replacing some of the just announced GRQ schedule.