Even if Naruto did get the other half of the 9 tails chakra \ power ....

Naruto power > 9 tails power.

(proven since Naruto took control of it, even though his mom helped)

Just picked simple #s for approx. calculations like a boss nerd

Naruto's power = 1.1

1/2 9 tails power = 1

So naruto, with full control of 9T is: 1.1 + 1 or 2.1

Adding the other half of the 9 tails chakra:

2.1 + 1 = 3.1

This is not anywhere close to double :\

Double would be a 100% increase in power (2.1 x 2)

He would get a max of a 50% increase in power (2.1 x 1.5)