Many myths are based in some form of fact. But that doesn’t make every myth true. For instance George Washington supposedly, in a myth(fable, legend etc..) threw a silver dollar across the Potomac and cut down a Cherry Tree but couldn’t tell a lie. We both know those are myths but his reputation preceded him enough that for a long time many people believed them. Such might be the case with the Philistines, they likely were taller than the Israelite’s but likely weren’t 9 feet tall. David certainly could have taken him out with one throw, and likely did cut off his head and traditions of the time did allow two opponents to settle a battle so the army’s themselves did not have to fight. However he probably wasn’t some child as is depicted in the Bible, and as mentioned Goliath likely wasn’t 9 feet tall, probably 6’+. Remember the Israelite’s, and many people for that part, back then were five feet or so tall.
Depends on your view of the bible. Goliath and his brothers were descendants from angel and human female breeding. They also had 6 fingers.
When young George lived on the Ferry Farm on the Rapahannock near Fredericksburg, the kids at the time would throw stones across that river. George had the reputation of reaching the other bank more often than anyone else...the start of the coin across the Potomac legend.