Looking at image depictions of Heligoland in WWI, there are three very prominent features that simply aren't there on the BF1 map.
1. A good-sized town on top of the cliffs, including stairways up to it.
2. Tunnel-bunker systems inside of the cliffs.
3. A huge industrial harbor area.
I could understand access to the tunnels and the town to be a bit of a balance issue, but they should at least be there as historical aesthetics. As for the harbor, that was very unlike DICE to leave out.