IMO the only reason Kurama was as strong as the 5 tailed beasts during the war was mostly likely due to Obito using their chakra to create 80,000 White Zetsu's. He only needed a portion of each TB's chakra to revive the Ten-Tails, so its only logical that he would of used 90% of their chakra to fuel his army.

The belief that their strength is based on the number of tails seems to really only be held by Kurama, something Gyuki didn't necessarily agree with, and somewhat demonstrated considering the Eight-Tail should have been able to easily over power Two through Seven otherwise.

Realistically, there isn't a lot o evidence, when the series began, that Kishimoto thought of having more than two, Shukaku and Kurama. In fact, as I can gather there really wasn't any talk of there being tailed beasts at all until Part II. So it was probably more or less Kishimoto just deciding, hey I can run with this difference number of tails thing.

btu didnt the chakra-consumption end after the zetsus had been created?

this wouldnt nerf them much :)

Agreed. Note that Obito was controlling 6 jinchuriki and their Tailed Beast. I simply don't see why it can't be attributed to this.

That's true, but Gyuki did hold Isobu in place with only three tails and simultaneously punch Kokuo away. I believe that Kurama is telling the truth, as he has already proven himself as being the strongest and the other beasts disagree because they don't want to admit that they're weaker than Kurama who also happened to be a major asshole to the rest of them. Kisame also stated that Gyuki was the second strongest for some reason, and those Kumo-nin were restraining Gyuki in that flashback they said "The Eight-Tails has more tails than the Two-Tails so it's harder too capture" which can be simply interpreted as it having more appendages to fight with. But it could also mean that since it has more tails it's stronger than the Two-Tails. So I think the tails are used to not only make them unique but to demonstrate their power, it's just that the difference in power between the others isn't that big compared to Kurama.

Tails show how powerful is Tailed Beast.

More tails is more to fight with. E.g. Kurama and Gyuki can use their tails as an actual shield. I just don't feel like putting much faith in one battle where half the Biju were under Obito's control. Considering the balance of power was kept with the Biju as-is (didn't the Sand only have Shukaku?)i think that in reality, the Biju are all roughly equal in strength.

Yea but Kurama's special power is raw power.

Each Biju has a special ability. Sand, fire, bubbles, lava release, etc etc etc. Only Kurama doesn't have such a power. He has a sensory power and his other power is just that: raw power.

They are based on Bijuu from Japan mythology, so probably that's why. In terms of Narutoverse - I think the number of tails represents the beast power, at least partly.

Only shukaku (Tanuki) and Kurama (Kitsune) are based on actual tailed beasts. Everything else is vaguely based upon other japanese monsters, but the whole number-of-tails motif is uniquely Kishimoto's addition.

@Thekillman My point was that they cannot all be equal in strength if Gyuki is capable of completely halting a raging Isobu with only three of his tails. I don't understand how them all being under Obito's control matters? The balance of power also gave each nation two beasts, and if you notice. Each nation has one beast with a low amount of tails and another with a high amount of tails which makes it almost equal. Iwagakure = Four + Five = Nine. Kumogakure = Two + Eight = Ten. Kirigakure = Three + Six = Nine. While Sungakure only had one because they didn't want another one but instead wanted more land. If they did get another one it would have been Chomei which would mean One + Seven = Eight. With Konoha having a single one and that one being the Nine-Tails who is also the strongest.

Kurama's special ability isn't raw power, it's his negative emotions sensing ability. Kurama has already been stated to be special compared to the other beasts and is clearly the strongest in terms of everything.