There is a nice use to it, with the very start of the game to get your band up fast. In midgame upon losing someone you don’t need to take it since you already have a leveled core. Now surely it would be better as a trait, especially since there are already traits that give 5-10% exp bonus making the difference not that big. But the fact that they do stack makes it even more valuable. A 30% exp boost is like having a level more every 3rd lvl.
As I already said it is an early game perk, and as such it is useful. And as I already wrote midgame and endgame it’s almost non existent. Now especially on hard the start is obviously the hardest and easiest way to power up is by fast leveling. Now since you do not have that much money and need to spend more for buying stuff, makes your party more vulnerable and you can not balance the odds with equipment. The other early game advantage you get is a faster growing captain class guy who gets the utility tree, or even two to have both t3 perks. The faster you get it the easier it will be. Now stacking it with a trait bonus makes you max out utility as fast as leveling ~4,5lvl without the combo. Instead of 6 lvls it might not sound much but thats a healthy difference on a hard mode game with a nice big spread out map.
Just for the record it still is only an early game skill. And it sure could be improved to last thru mid and maybe even endgame. The question is, does it need to? As it is now I do find it balanced, and I did test it to see the difference with my testing party. It is a t1 perk afterall. Your suggestion is a good one but it would only strenghten it’s importance early game maybe even make it too strong. +10 to every stat at lvl 11 is quite effective. It would make it more valid perk, but only at level one and make it more discouraging at higher levels…