Naruto Chapter 420

[Yukimura]

Naruto had shitty chakra control up until around the time he did the tree training, then he got a little bit better, then he started the walk on water training, and he got a little bit better, then he learned the Rasengan, and he got even better still. The fact that he couldn't do those things and then learned to do them demonstrates that his ability to control chakra has improved as the series has gone on. From what you've said it seems like you don't think Naruto has made any progress at all between chapter 420 and chapter 1. Perhaps it can be argued that he's made the least progress of anyone but I don't see how you can justify saying "his chakra control sucks" using "way back in part 1 he had problems controlling his chakra" as the basis for your assertion. It's like you'd make the point that the Naruto in chapter 1 was able to do all the same things with his chakra that the Naruto can do now because his ability to control chakra hasn't increased at all.

As to technique strength correlating to technique creator, look at what Sasuke has done with Chidori. Kakashi has never demonstrated that he does anything with Raikiri but stab people with it, but Sasuke has taken the original idea and created two new, and I would argue more useful, variations on it. Whether Sasuke's version of the original technique is 'stronger' isn't something I think we can reasonably judge but if I had to choose between being able to do Kakashi's Raikiri and being able to do Sasuke's Chidori, as well as Chidori Nagashi, as well as whatever he calls it when he throws it I'd definitely choose Sasuke's line of abilities for their versatility.

I agree with your assessment on the Rasengan however, the highest compression ratio and rotational speed is going to have the highest destructive power. Still, I think the fact that Naruto uses two separate minds to create his Rasengan raises the possibility that his could be more powerful than a single mind Rasengan in the same way that a dual core processor has better performance than a single core processor when computing two unrelated things. No matter how good one's chakra control is, outputting a steady stream of chakra and rotating that chakra both compete for mental resources, thus doing both at once would be less efficient then being able to do them in parallel on two different platforms.