while testing, if you wear mpt fatigues with a carrier lite you can take 2 chest shots or 1 below waist shot.
While wearing pilot coveralls/csat ghillie, you can take 2 chest shots and 2 below waist shots, meaning you can survive 1 extra bullet to the leg and it could be the difference between life and death, so no. its not only cosmetics, please do research before adding stuff like this. go into the fucking game and check out how many bullets you can take before you die with each piece of clothing.
EDIT: To mention what @Haych said you can also still fucking wear pilot w/ carrier, so fix the script, and remove csat or give it to everyone, it may not be a huge difference when it comes to shots not in the chest but it does matter between life and death.