I could accept than the idea of rebooting (yet again) the Legion was more from DiDio than from Bendis himself. Waid revealed than he had no intentions on causing a reboot of the Legion but it was the editorial office who demanded it. And who was there? DiDio. However he share the blame because one, he could had rejected the idea (and I doubt DiDio would had say "No" to his new Ace) but he choose to keep the ball rolling (less investigation work, I suppose), and two, the guy sold himself as the guy who came with the idea of rebooting the Legion again and doing an "Ultimate" Legion.
Maybe not the what, but the how? The guilt in on Bendis. The problem with Jon is not only the aging but the how. It always has been argue than the upbring of Superman has been pivotal to his moral development. What upbring have Jon? A five year trauma and torture by a guy who is identical to his father. Five years. On an important development moment. And the kid acts as if nothing ever has happened? If there had no consecuense to this problem this causes two problems: or you admit than Jon is ok because his kryptonian influence, that makes the importance of Superman upbringing with the Kents diminished; two, if you don't that openly then you are going to send Jon on the represion route and that never is a good path, because you are giving the excuse to create a psychotic Superman. You are giving an excuse to have a Superman with a deep trauma and considering how repeated has been the trope in the media, this path could be a sad rout for Jon to follow.
Bendis has some good ideas, some bad ideas and some horrible ideas. And in his time in DC it seemed like he choose to developt more the bad and horrible ideas than the good ones. His runs had been not boring but irrelevant and if he will be remembered will be by the twists and publicity stunts than for a good development of the characters. Indeed Naomi was among the good ideas, but she failed as a live action adaptation and that is a crime than modern media punishes highly.