That the prophets of the Old Testament lived concurrently (that means at the same time).
God didn’t wait until the old one died to get a new one like the latter-day-saints do know.
Hebrews 1:1-2 has changed the way God spoke to us in the Old Testament.
1 In the past God spoke to our forefathers through the prophets at many times and in various ways, 2 but in these last days he has spoken to us by his Son, whom he appointed heir of all things, and through whom he made the universe.
It appears He also chose to speak through Paul. Right? It doesn't say that "he has spoken to us exclusively by his Son..."
Neither did I say that God speaks to man through one person at a time. You have proffered a non sequitur. In fact I am grateful that along with the living prophet today, there are also apostles who serve and speak the words of the Living Christ.