3-5-2, 4-3-3, and 4-4-2 are the main formations, but each has several different ways to line up and different tactics within it that are more varied than the NFL's man, zone, and hybrid schemes. I'm not saying every 4-3 zone defense is exactly the same, but there is much more variety in a soccer 4-4-2 than in an NFL 4-3. In soccer, just with a 4-4-2, a team can play a flat 4-4-2, bucket 4-4-2, diamond 4-4-2, empty bucket 4-4-2, 4-1-3-2, 4-3-1-2, are basic differences in how the players line up, then you can get to differences with player symmetry in the midfield, using a false 9 or not, using a strict holding midfielder, using a pulley system with two central midfielders, how much defensive responsibility a central midfielder or midfielder at the top of a diamond has, how much the forwards are expected to press, how much the outside backs are supposed to press or counterattack, if the goalkeeper should act as a sweeper, if the central defenders should play as midfielders with the ball or just try to pass it forward, if they should hold a firm line for an offsides trap, how wide the outside midfielders should be and if the fullbacks should overlap them, if the outside mids should cover for the fullbacks or if the 6 would drop closer to central defense and have a centerback go into the space left from the fullback, what defensive responsibilities the outside midfielders should have, if the outside midfielders should drift in or stay wide, if the ball should be played wide and crossed or played through the middle... That just includes a 4-4-2 and it's offshoots. There is just as much variety in a 3-5-2 or a 4-4-3 or potentially a 4-2-3-1 if that's considered wholly different than a 4-4-3. NFL base defenses can't sniff that level of variety in tactics.