I dunno, I thought Ryotaro was a better-realized character than Wataru. With Wataru, I got the feeling a lot that the staff knew they could take him in several directions and never quite settled on which one.
Ryotaro's character growth didn't seem very well "displayed" though. Even though it seemed in "Saraba Den-O" that Ryotaro finally discovered his inner bravery or something like that which made him appear to have a nutsack.......there was still some aura that he gave off where it appeared that Ryotaro will still collapse on the floor when someone pushes him with their index finger.
Wataru, despite the crazy directions that he was being pulled around throughout the entire series, his growth seemed a lot more displayed IMO. I mean, he's had his moments where he regressed back into his little ball of shame, but he always seem to come out even better than before he shriveled himself up. Especially in the last few episodes of Kiva (still didn't like the Time Travel crap), they showed Wataru as a true changed man. Wataru displayed an aura, a swagger, determination.........everything that is a result of his character growth. To some or a few, it may have felt sudden.........but after seeing his own father risk his life for him (or whatever life changing **** he went thru during the Time Travel), it caused Wataru to completely fix a majority of his mental flaws and he came out to be a more stronger, confident man.
To be honest, that's how most people usually begin to change themselves in real life. Life changing events such as a father risking their life to protect their kid or seeing the person they love die in front of their eyes, it can definitely result in a dramatic change in a person's confidence.
Not to say that never happened to Ryotaro, I mean......his sister's life was in danger towards the end of the Den-O tv series as I last recall, so it caused him to undergo some change as well. But Ryotaro's change didn't seem very well executed as Wataru's, where you can clearly see in his body language that he truly changed.