They absolutely should not get rid of any D-Leagues.
I have a Possession WR who was Regional Minor level this season. He wasn't going to be useful this season to any human team and I knew that because I had to work on his majors first which left him well too slow, even with all his equipment in Speed, to be useful to anyone. I certainly wasn't going to try to market him. Someone even asked about him (his stats were closed) and I told him how slow he was, said I'd sign if they still wanted him, but advised them to look elsewhere. They made the wise choice not to sign him, so he played in the D-Leagues.
Had there not been D-Leagues his level, I'd have had to screw over that team or otherwise finagle him onto a human team's roster. It was much more right that I was able to be a nice guy and honestly say that my player couldn't help them.
This season I did start filling up his Speed, and he'll be on a human team (the deal's already been worked out) for next season. He'll still be slow even for his level, but not so ridiculously slow as to be useless. But the D Leagues need to be there, among other things, for non-Speed archetype players in Speed positions.