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
Now it's Ariete bashing time. The Italian engineers had no knowledge of manufacturing proper tanks (even the OF-40 export tank was largley based on Leopard 1 components; in fact the original hull design was made by German companies), so the Ariete is a bit special. It's turret has extremely thin side armor, some say it's spaced armor, other people claim it's normal steel armor or composite. Judged by the thickness of the ammunition hatch, it's side armor might be 100-150 mm thick.