How did the Late Avars and arriving Magyars supposedly merge under the double-conquest theory?

The "double-conquest" theory, proposed by archaeologist Gyula László, suggests that the creation of Hungary occurred in two distinct waves rather than a single migration in the late 9th century.12

According to this theory, the first wave of conquerors—the Late Avars—arrived in the Carpathian Basin around 670 CE. László classified these people as "Early Magyars". While the Avar dominion was later crushed by Charlemagne around 800 CE, the theory posits that many of these Late Avars survived the 9th century. When the second wave of Magyars arrived in the region under the leadership of Árpád in the late 9th century, these surviving groups supposedly merged with the newcomers to form the Hungarian people.12