I haven't really had a problem despite not using either Fang or Hope, who are considered the best attacker & magic user respectively. I don't think it's a massive issue to select an exact party - so long as you have one that does what you want. I love Tri-disaster, so Fang is useless in my party. I also like to take a lot of risks against enemies who can quickly diminish my health, so Hope is out the window as his HP is the lowest by some margin. I like a balanced party not in "highest of everything" but rather a "red mages everywhere" style.