My ideas...
Genjutsu: I was thinking about genjutsus effect. Most ppl use kai release or stab themselves to get over the genjutso. What if the genjutsus effect is to increase the amount of other jutsus dmg with some %..
for example:
d-rank - 30%
c-rank - 35%
b-rank - 40%
a-rank - 45%
s-rank - 50%
so if s.o uses jutsu that has 30dmg + genjutsu,the opponent will receive -
30 + 35%(30) = 30 + 10,5 = 40,5 dmg
If the opponent uses defensive jutsu - he will block the main atack, but not the dmg bonus from the genjutsu - in this case 10,5 dmg.
Replacement jutsu:
I dunno if there is some rule for this jutsu, but it can be used many times to dodge the attacks. So what if the replacement jutsu only reduces the amount of dmg to 1/3 of the jutsus dmg. So if s.o uses jutsu that have 30dmg and the opponent uses replacement jutsu, no matter what he will receive 1/3 or 10 dmg.
The %-numbers may be changed, that are just examples. I know most of you won't agree with my ideas, but I think that will make the fight more balanced.