Whether Samsung ever had a "high priority" setting in their messaging app or not, there's nothing in the SMS protocol that it would affect, and carriers don't change the speed with which they send an SMS based on what Samsung says.
Email has priority settings, but that's a holdover from so long ago that you probably weren't even born then. The priority of an email message is ignored now, and has been for a long time.
If you want high priority, use a regular phone call.