I haven't actually played the PnP d20 Starwars but I have played a lot of other PnP d20 systems. Humans have average stats of 10 so a 15 is quite heroic. I have played PnP Starwars with the d6 system. Although Mandalorians would prossibly have a higher Str and or Con than humans due to their war like nature.
When you say that Dex is useless because of the Dex bonus restriction of the armour that only applies to AC, not every other Dex reliant skill / bonus.
As a leader he would certainly need a reasonable Int to analyse battlefield situations quickly and rationally.
He'd also need the higher Wis to represent willpower and perception which is what it applies to game mechanic wise and to also help make his decisions the right one and not something rash.
The Cha is for personal presence and personality. Without it he'd probably be too introverted or abbrasive to be much of a leader.
His high Str and Con would represent his physical power and hardiness that the Mandalorians respect.
If you look at him from a Rollplaying or number crunching perspective then you're right. You could have just left all his non physical stats at 10 or less and put the other points into the physical stats. As it is, it looks as if he'd only be all that good as a melee or backup ranged character. Not sure about KotoR2 but the Mandalorians have regeneration in Kotor 1 so the lack of AC could be countered by that.