General

Critical is not affected by CA/ACA
~ ACA maxed first
- raging blow maxed first

1 SP in both ACA (or none) and raging blow
Lv 1 RB : 665%
Lv 1 ACA or Lv 20 Combo Attack : 25%
Total damage percentage: 831.25%

-(Lv 3 RB): 695% * 1.25 = 868.75% (crit adds 69.5%)
At 6 SP in either one of the two skill
~(Lv 6 ACA, Lv 1 RB): 665% * 1.36 = 904.4% ******* (lv 20 Intrepid slash = 979.2%)
-(Lv 6 RB): 740% * 1.25 = 925% (last hit crit adds 74%)
-(Lv 9 RB): 785% * 1.25 = 981.25% (last hit crit adds 78.5%)

At 12 SP in either one of the two skill
~(Lv 12 ACA, Lv 1 RB): 665% * 1.49 = 990.85% ******* (lv 20 Intrepid slash = 1072.8%)
-(Lv 12 RB): 830% * 1.25 = 1037.5% (last hit crit adds 83%)
-(Lv 15 RB): 875% * 1.25 = 1093.75% (last hit crit adds 87.5%)

At 18 SP in either one of the two skill
~(Lv 18 ACA, Lv 1 RB): 665% * 1.64 = 1090.6% ******* (lv 20 Intrepid slash = 1180.8%)
-(Lv 18 RB): 920% * 1.25 = 1150% last hit (crit adds 92%)
-(Lv 21 RB): 965% * 1.25 = 1206.25% (last hit crit adds 96.5%)

At 24 SP in either one of the two skill
~(Lv 24 ACA, Lv 1 RB): 665% * 1.81 = 1203.65% ******* (lv 20 Intrepid slash = 1303.2%)
-(Lv 24 RB): 1010% * 1.25 = 1262.5% (last hit crit adds 101%)
-(Lv 27 RB): 1055% * 1.25 = 1318.75% (last hit crit adds 105.5%)

At 30 SP in either one of the two skill
~(Lv 30 ACA, Lv 1 RB): 665% * 2.00 = 1330% ******* (lv 20 Intrepid slash = 1440%)
-( Lv 30 RB): 1100% * 1.25 = 1375% (last hit crit adds 110%)

Conclusion
Maxing Raging blow first is more efficient than maxing ACA first.

lv 6: 6 orbs, each adding 6% damage
lv 12: 7 orbs, each adding 7% damage
lv 18: 8 orbs, each adding 8% damage
lv 24: 9 orbs, each adding 9% damage
lv 30: 10 orbs, each adding 10% damage

I've tried levelling it, and what you said is true as far as I can tell. I'm guessing the "Max Combo Orbs: 2" states how many orbs you charge up on a double proc chance.