In a 3 man crew it is the TC that would tire more quickly. Behind the fighter pilot, the TC is the most overburdened job in the military, you have to scan and engage targets, communicate with your crew and other tanks, analyze the situation, and usually do this all at once. With a fourth crewmember, scanning and communicating is much easier. When the loader isn't loading shells, he's working the radio and looking for targets. Not to mention maintenence, hauling tracks, armor plates, ammo, fuel, is very tiring and having a 4th guy is handy.
One thing I hate about Leclerc advertisments is they claim that it is the only tank with modular armor. That is bullshit, the Abrams and Merkava both have this. How do you think they upgrade the armor? Also, the FINDERS system on the Leclerc is pretty much the exact same thing as the IVIS and TCCS.
But Eric is right no western tank has any big advantage over eachother. What it comes down to is skill, training, and the commanders.
And all western tanks are more accurate on the move, at high speeds is when the gyro kicks up, even the Bradley is more accurate moving