This is pure irony. Both MyGM and MyLeague are "story-modes" as much as MyCareer - at least up to 2K11 where MyCareer started more and more to be a "roller-coaster" experience than a "sand-box" as it originally began in 2k10.
As Leftos stated ai mechanics and systems for the majority of the game should carry through all modes - gamewide. Improving team development translated from Leftos' improvements in all three modes I'll be playing this year.
Story-boarding MyCareer into an on-rails experience is one direction that may attract some but it turns off a lot as well. Think of it as being Skyrim vs Dragon Age Origins, and the industry-trend is to expand on the sand-box experience not the on-rails experience. Bungie followed your philosophy and they are receiving a lot of criticism for small worlds and what seems like a very scripted experience. 2K should be very aware of this themselves.