He was overpowering at close range. Had they no archers? Could he simply dodge all arrows, or did they simply bounce off him harmlessly?
So many unanswered questions....
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.