I'm not sure comparing those two is really that useful. Wouldn't a large scale military invasion have vastly higher logistical requirements than sending out a

I'm not sure comparing those two is really that useful. Wouldn't a large scale military invasion have vastly higher logistical requirements than sending out a purely exploratory party? Afaik many Roman soldiers were also quite wary of going to Britain, a land they considered even more foreign and savage than Germania, which probably added to the Roman struggle of gaining any foothold.