It’s an historical question. It is my understanding that the convention for current flow being that of positive charge occurred before electrical current was really understood. So in electrical engineering it’s the convention that stuck. Physicists don’t care for it since we now know that most current is the flow of negative charge, electrons (semi conductor currently being one exception). Bottom line: It doesn’t matter as long as we’re consistent.
Read that Ben Franklin in static electricity experiments knew there were two types of charge depending on what materials you rubbed together. He thought of current as a fluid which if built up too much , became too “positive”, it would discharge causing a spark.
If this true, then it has nothing to with positive charge going in one direction being equivalent to negative charge going in the opposite direction.
Hope this helps
P.s the above is from “The Direction Assigned to Electric Currents” NASA website Here is the link.https://www-spof.gsfc.nasa.gov/Education/woppos.html