Merlin typically needs some sort of hand movement in order to cast a spell, unless she pre set something (which wouldn't make sense in that context). So that explanation makes no sense.
Hell, she
doesn't even have her sacred treasure here.
They make the
distinction themselves when Meliodas' curse is broken and SD's isn't.
Also, SD was in another dimension at the time.
You're just arguing the subject with the subject here. We know she brought back the curse; the argument is whether or not she was the one constantly resurrecting it.
It also never supports your notion at all. In fact, the curse automatically disappears anyway when Demon King finally dies, suggesting that it's completely tied to his existence.
My argument is that the curse was completely tied to DK still. All she did was re-established something that was broken, but not technically gone forever and still tied (as before) to DK's existence.