Before I shift this post to being about, you know, Ninninger, the Sentai with the name in the thread title, I will chime in my 2 cents about Daigo.
I didn't dislike Daigo because he was "pretentious" (because being pretentious would actually be a character flaw) or "too" perfect. I didn't like him because he was boring in his flawlessness. Out of all the story arcs the Kyoryugers had in the show, I thought his (and Amy's) were the least interesting, namely because Daigo never really grew as a character. And why would he have to grow, he's already as great as the show wants him to be. I believe flawless characters are just boring. They don't have any problems to overcome because they face everything with a smile, have everything they already want, and there's never any doubt they won't win.
Now, allow me to explain why this means Takaharu is an even WORSE character than Daigo. At least with Daigo, I could (begrudgingly) buy him being the bestest guy ever because the show goes out of its way to show us repeatedly that he's great at everything he does. The show even blatantly goes out of its way to tell us he's perfect while he's training. With Takaharu, we are only TOLD he's great at everything he does. The other characters point out his flaws, but there's never an attempt to prove on them. He's stupid and reckless, but it's okay for him to be stupid because...reasons? Hell, early on, we see him struggling to master the ninja arts. Then a few episodes later, not-Juuzou for some reason believes Takaharu is the only one who can beat him. And he's right, even though at that point, Takaharu was one of the weakest ninjas except for his pure tenaciousness....or something. And then Takaharu proceeds to beat him by himself, something the show has decided its okay for him to do repeatedly.
Daigo is also simply charismatic. Ryo Ryusei pulled off the role really well and he was honestly given much more substantial stuff to work with. I didn't like the material personally, but compared to Ninninger, it's downright inspiring. Now, Takaharu's actor, Shunsuke Nishikawa, is having BIG difficulties pulling this off (and we're halfway through the series at this point, so it's now certainly a lost cause) because it's clear he's not as comfortable working with this kind of material. The material itself isn't that great (his try-hard catchphrases, the goofy dialogue) to boot.
TL;DR Kyoryuger earned it, although I didn't care for it because I don't like that type of storytelling. Ninninger hasn't, which arguably makes it even worse.