Low life growth is not only expected, it is necessary for such a powerful character to keep him balanced. We are getting a classical glass cannon character this way. It also prevents you from maxing his attack on low levels so that you can't sweep all 2 star users with one hit without risking him dying too early.

Yes, I am only looking at it from the game mechanics standpoint, I have little interest in Naruto as an anime or world.

That being said I am very much okay with him staying underrated I really do not need any more serious opponents on my server.

Well your theory is plausible at least or at most, depending on how you look at it.
I guess that's good enough considering there never will be any confirmation on this. A bit of theory crafting never hurt anyone though, as long as it makes at least a tiny bit of sense.
Btw I actually prefer Ukon Sakon to Ukon and Sakon, sounds better in my opinion.