He has two major points in the game in which he is the best.

The beginning (60 Sphere Levels or less), which means you send him wherever you want, (making him a better version of his Doppleganger) and the ABSOLUTE END, which means 50k+ HP + Celestial Weapons and 255 stats. Since his stats are spread out over the place, you won't have to worry about removing any +1 stats and having an impact on Kimahri, since all of his stats are stopped at 255. Everyone else will have some sort of unbalance, or wasted points.

Let's say I remove a Defense. E.G:Yuna's Def will drop to 254, Rikku's to 253, and Tidus' to 250. If I removed MDef, then Auron's would drop to 248. This does not affect Kimahri, because his stats were so spread around, that you would have to remove multiples. This also means less wasted points for characters. Auron's Stg starts at whatever it starts at, for the sake of argument, let's say 50. Kimahri starts at 30. If I raised both to 255, then I would waste 20 STG points on Auron (5 nodes) to get Kimahri and Auron to the same point, since 255 is where the stats stop. (They actually stop there, anything past, will result in simply having to remove more nodes to see a decrease in stats). His Luck is also the second Highest, which means you won't have to fight as many battles to get his Luck to 255, unlike everyone else.

Kinda hard to explain, but I try. He however, sucks mid-game (when everyone's stats are around 150; his stats will remain the lowest until 255, when he is once again, equal)