If your 1st slot is a combo starter (ex. Sage Naruto, Mei etc..) then OF COURSE u wanna max initiative on him/her.. Your enemies may already be paralyzed or whatever so they can't combo after you
If your 2nd/3rd/4th is a combo breaker (ex. Ao, Shurado etc...) it's still good if they have high initiative but it doesn't need to be the highest. The ideal situation is for u to attack them with a combo starter first (Sage Naruto) and then use a combo breaker to stop them from fighting back.
If they are just support characters (ex. healers, fire main 2.0), it's not really THAT important for them to have high initiative.