Bapto comes from classical into koine.
The NT certainly uses baptizo in terms of affusion (Holy Spirit outpouring, washing of hands) and of sprinkling (Children through the Red Sea and Noah in the Ark)
FWIW, the actual Greek word for immersion is "buthiso" or "embuthiso" (bythiso)
It doesn't include the idea of dipping or washing as does baptizo.
The Greek word "buthiso" is translated as "sink" or "drown" in the New Testament. While the idea is similar, it seems to denote something that is plunged deep and not raised back up. That does not fit Christian baptism. That is the reason the word "baptizo" is used.