Legacy achievements are back yet again. Thankfully simming is pretty quick this year so it shouldn't be too bad. If you follow these instructions you should be able to pick up all achievements in around 5 minutes.
1. From the home screen, go to the customize section. Customize > Share & Manage Files > Download Community Files.
2. Search "Dallas99" and download the roster.
3. Back out to the Share & Manage Files screen, select Load & Delete files, load your new Dallas99 roster.
4. Go to the "Play" menu on the home screen, select Franchise, Cloud.
5. Start a new franchise, and select use active roster.
6. Let the roster import for a few seconds, then select the Cowboys.
7. Under league settings, change the following: Skill Level > All Madden / Re-Sign Players > ON / Progress Players > ON / Sign Free Agents > ON
8. Save settings, now go to select role - Coach > New Coach > Team Builder > Accept & Continue
9. Now start playing the new franchise.
10. Select Advance Week > Jump Ahead: Sim 10 Years
I unlocked all achievements around year 3 or 4. If anything is unclear, please let me know in the comments and I'll be sure to change. Enjoy.