You may not be taking into account that Sampson was God's man of the hour and was supernaturally equipped. If God gives you a job He will equip you to do it.
Another thing we don't know is "How many Philistines were Nephilim? The Anak brothers were working with the Philistines during the days of King David and Goliath. Saul was during the time the Nephilim were supposed to be killed on sight out of Israel. Many of the "Canaanites" were still giants after Joshua took the Promised Land. Joshua just quit fighting after 7 years and declared victory, leaving many giants in the land for later conflict, including Gaza, where the Philistines were.
The men Sampson killed may have been giants and he needed God's strength to do it.
Remember the bad report the spies gave on Canaan. It said they were grasshoppers in their eyes and they devoured the inhabitants of the land. These giants were cannibals. God said He had given them the land already, but the giants frightened them. When you read in Scripture that they "utterly destroyed" someone, they killed them, piled them up, set them on fire, and then put stones on top of the bones. God flooded the earth to kill these giants. After the flood, Nimrod was the first giant to return. God has had "open season" on Nephilim since the beginning because they are not in the image of God.
Your points are sensible. But swinging a jawbone 1,000 times takes time, regardless how supernaturally equipped one is. Of course, perhaps he swung it only once and somehow the force of that swing killed them all—God could have done that. We just don’t know.
When you start digging around, there were a lot of giants during the Old Testament times.
If any giant relics were found now, they would have to conceal the evidence because it would support the Truth.