I think Suikoden IVs battle become a pain since the best rune cannon users are non-autorecruits (Jeane, Ted, Warlock, Konrad come to mind).
Yeah,that's why i'm saying it.
The best mage available will be Pablo if you use only auto-recruits...but it would be a better choice to put him in Elenor's special team,in order to defeat Graham Cray. So the best solution is to use the 4 knights of Gaien in the rune cannons,who are mediocre rune cannon users.
Here is a fine formation for the last battle with only the auto-recruits:
Seperate Task Force:
Rune cannons: Tal (Water),Kenneth (Fire),Paula (Wind),Jewel (Lightning)
Rune cannons: Sigurd (Water),Tov (Fire),Desmond (Earth)
Rune cannons: Yu (Wind),Setsu (Lightning)
Rune cannons: Agnes (Lightning)