Well, if you include TUSK as armor kit for the Abrams, then you also have to include the different Theatre Entry Standards (TES) armor kits (three versions at least) of the Challenger 2. The base armor however was most likely not upgraded.
The Leclerc is not geometrically more efficient. It could have been, if it's armor layout wasn't designed so badly. The Leclerc trades a smaller frontal profile for a larger number of weakspots. It uses a bulge-type turret (no idea about the proper English