Byrne never was, nor is, the most diplomatic creator. And in his perspective he wanted a more essential Superman, free of baggage. Was it for the best? Maybe not, but marked an era. However, I believe he said in some moment he did regret having erasing Superboy, and at least he was conscious of what erasing Superboy could mean for the Legion. And he was willing to work with Levitz to give the Legion a explanation, with the whole Pocket Universe from the Time Trapper. Maybe that aspect was not something Byrne encouraged but buit it was a path than the editor (Carlin?) choose to follow and stand for.
I mean, several times we blame certain decisions on creators, when maybe the order or direction came from higher spheres. I even are willing to think than this last reboot was not an initiative of Bendis, but something than DiDio wanted to stablish: a teenage Legion.