Try to use naruto six paths as your move 3 ninja to see how high is the damage he lands on your enemy move 2/3/4 of comparable power with you and how big, consequently, is his self heal. At that point you'll have more or less a good idea of how less useful than now he is when you'll begin to face people with 3/4 moves almost as much stacked as move 1.

It is like is in arena, with the difference that the healings and shields, outside arena are not that useless as they are in arena. (in arena you hit for 2k with mystery and 1k with standard. They heal back 800. Outside arena on comparable power you hit the same 3/4k but they heal back 5k, just to state it more clearly).

His point is that as we move later into the game people 2/3/4 equips will start catching and all 4 slots will be on a more even footing, making the "carry" ninjas of the current meta a lot weaker as they can no longer blast the back rows into oblivion. It's at that point we'll just see a shift to a different meta. This is ways off anyways, as even the mega whales are only midway done with their slot 2 (a lot of them have finished slot 1). I call a year or so till we start seeing meaningful numbers of players with multiple high power slots.

Let me rephrase it.

How high is the damage naruto lands on your enemy move 1 if his move 1 is as much stacked as yours? Then multiply that to 4 and you'll have your answer.

Why madara 10 tails costs that much?

Because when you are in that kind of situation the 30% boost to nin and atk and the SUPPRESSION OF IMMUNITY are good (and so is the selfdodge he gives to himself that has no limit per round and applies to every kind of attack).

The set of abilities of those ninjas are not thought for our current bp balancement.

So, yes, right now he is not good because move 1 rules, but next year he will be (if the game is still lively...)