Call of duty is the easiest of the bunch by far. But Battlfield absolutely does not take more skill than Halo.Its true breh.
Battlefield takes alot more than just killing other players to be successful, tons of different factors involved in all aspects of gameplay. Its why call of duty players hop on and get murdered and complain about vehicles and map sizes and shyt.
Plus the fact that the gun game has so many different variables involved from bullet drop and damage related to distance plus recoil and how your gun acts different depending on different movement fire rate and terrain.
Halo feels like a watered-down quake, its all about getting to the good weapon first and controlling the best part of the map, but i guess simplicity is exactly what halo fans want.
Bullet drop and variable damage exist, but they don't really make the game harder. The overwhelming majority of kills come from whoever the first person is to spot the other player. You don't have to be very skilled at aiming to get kills. The "skill" in battlefield comes from knowing the map layout spawn points, and other players tendencies.
And while power weapons and map control are a big part of halo. The kills come down to one on one skills. Don't matter what weapon you have, or where you are on the map the skilled player will prevail in Halo.