The railroad plan or Transportation Plan was very important. That plus the deterioration of overall capability caused by the Oil Campaign were very impactful on the flexibility and resilience of Germany's war machine.
I'm not arguing that so much as the fact that D-Day, while a huge milestone, wasn't as big a deal as Big Week for wrestling control of the air from the Luftwaffe. Re: D-Day importance: the episode where they are at the Flak House and oxford has the reference to a Second Front and the Woodie Guthrie song which are explicit signifiers D-Day's importance.
I will offer another criticism that was mitigated somewhat by Cros' affair with Westgate, he comes across as a bit too "I was just doing my job" while everyone is offering up hosanas to his superb navigation skills. I mean, it does help to base a show or movie on a memoir if the memoir is somewhat self-deprecating.