I don't really want to debate yea or nay to greatcoats.
Did they wear them in April 1918? -yes.
Did they wear them charging across no mans land in 1918? - I don't know but unlikely.
They wore greatcoats but often soldiers preferred the leather jerkin and/or woollens* in the assault in rainy and/or cold weather. The greatcoat did trail in the mud and get weighty so the hem was taken up and the groundsheet was also used (like a cape) in wet weather but these would be for a more static role not for a sprint. The uniformity is not in keeping with the late war and I would have liked to have seen a mix of uniforms and poses. The bomber would have been better depicted with a Mills bomb as far more typical though an inert potato masher could be and was used as a cudgel. The cotton bandolier was plain though these look like cavalry/artillery types.
* 3 layers rule with the sleeveless jerkin as an addition