Paying two action dice up front to earn half an action die per turn is too much to make Aragorn worthwhile in most cases. He costs at least two up front because of the seperation costs. Also, in this context he never produces character dice, does he? Ouch. No, I'd probably keep him in the Fellowship.
The normal Aragorn takes two actions that could be used for the fellowship, and statistically gains them back in four rounds of play. At the same time he gives two additional "military" actions.
My version takes one action for separating which could have been used for the FSP and one muster action for promoting. Aragorn will never gain the fellowship action back, but will get the muster back in 2 rounds and in the next two rounds he will have gained 1 full military action. Yay, we are at the starting point actionwise! Two actions behind the normal Aragorn.
Ouch indeed... Aragorn is lousy ATM. Actually, using CAT for separating would even it up somewhat. For how many rounds is Aragorn in the play usually?
Aragorn needs either a boost in his fighting skills or in his token's power or both. His token could almost givefull actions of army/muster die. (It wouldn't really matter then if you use a token or preset die, but whatever.) Aragorn's death would still be affordable (at least with improved fighting skills), because he doesn't help FSP.
As an afterword though, my version and the normal version of Aragorn aren't directly comparable, because the fifth die is already in play usually, and the sixth one is kind of divided between GtW and Aragorn instead of them giving a full die each.
How OK is it to give them a combined power of say 1,5 dice? These being not directly usable for the FSP. (In terms of moving companions and separating and maybe using certain cards Gandalf is saving the FSP some amount of recources.)
I'd suggest letting him spend his action token to move or attack with 'his' army. This is stronger than you might suspect. I had to nerf a similar attack ability from a draft because it was too strong.
Frankly, I'd suggest the same for Gandalf the White's token.