Tetsuya's status as an Ace Pilot can be used as an explanation for so many weird things that happened inside the series and Super Robot Wars. For example, while Great is superior to Mazinger Z, it has more variety of weapon, including the Thunder Break, making it rather impractical to mass produce, while in comparison, Z's clone has always been splitted into several parts(the Mazinger army, consist of several robots each carrying one of Z's weapon) but Great's clone is an imperfect replica with Thunder Break and Atomic Punch. The reason ? first, Kenzo is a much more superior scientist to Gennosuke, which make the creation of superior weaponry easier. Second, unlike Koji, who relies on chance, and Combat Pragmatism, Tetsuya's fighting style involves the practical usage of his own weapon(for example, the countless variation of Thunder Break). Since Tetsuya's fighting style as an expert is more simple and consistent, it makes it FAR easier to copy and analyze.
When Prof. Kabuto died, he asked Kouji he took care of Shiro and tried to get along with Tetsuya... but he never mentioned Jun, who also was his adoptive daughter! Kenzo's parental skills always were arguably, but... Jun got along just fine with everyone, understood Tetsuya better than himself, and was doing a better work putting her act together than Tetsuya. So maybe he thought she would do fine and he did not need to worry about her — he had no doubts about how strong she was in all fields, whereas he was aware of Tetsuya's horrifying insecurities Beneath the Mask, likely felt that he was at least partially responsible for them, and was sure that Tetsuya would completely break down. And yes, Kenzou was right.
When Shiro finally learnt Kenzo was his father, he refused believing it. That reaction was understandable even if you do not keep in mind that, in episode 90 from Mazinger Z, an android impersonating his and Kouji's mother appeared and he totally bought it then. Considering that Kenzou was part-android at that point, upon learning that he was their dad Shirou immediately and very logically believed that he was being tricked again.