power becomes harder to get the higher you go, so a 9k bp difference with him stacking his m1, would be a much bigger difference if he wasn't stacking.

also consider, if his m1 had 25k injury, but his m2/3/4 only had 10k, but all of your ninjas had 15k you may have much more injury on your ninjas than his back line which helps close the bp gap, but since the difference is so much smaller comparatively it feels like you don't do much damage after getting 1 shot., also remember the higher your crit the more often u crit up to 95% chance, so if ur not critting u it for even less than his m1 is since hes critting 95% of the time vs your 20%?, which is again a huge difference.

the current power features heavily support stacking just 1 ninja and using the other 3 to buff it, or who have some special feature to give u that slight advantage, edo itachi to reduce nin dmg and cc an enemy or edo minato for the barrier to prevent chakra gains. against a s06p naruto, u WANT your backline dead so he wont heal off them, which makes stacking an m1 an even better idea.

nerfing injury wont solve the problems, because later on, ninjas have so much hp that u cant kill them easily, so u need that bonus crit dmg or u will never be able to kill 1 enemy ninja. while saying that might make % tactics sound like a good idea if we nerf injury, it ends up having the same effect as leaving injury without the % tactics at higher bp and at lower bp things just die to whoever is faster with ninjas like edo hiruzen being more op for their raw dmg

what is really needed is power features like 5 natures chakra, which gives a % of ur m1 stats to the rest of ur ninjas on top of giving them their normal amount of stats when u work on them, so the m2/3/4 end up getting more stats total than the m1, but that would require tweeking so it can be finished on the m1 sooner to let the m2/3/4 actualy have time getting the stats, but again with the current feature set people would rather get less power and stack it onto the m1 for more results.