A good argument could be made for delaying the lander until surface conditions are understood. Having the lander die by being impaled on ice spikes during terminal descent would be double-plus ungood. But if delaying the lander, hopefully there'd be funding for instrument development and landing strategy studies, so some some of that risk can be bought down in the early, less expensive stages of such an ambitious project.
I think there are a lot of hidden risks that are not readily apparent--and by "risk" I don't mean simply "the spacecraft crashes" but more like "the spacecraft fails to perform the mission." What I've heard is that some of the instruments might be pretty difficult to design to return the data that you really want. So as you note, it might make sense to delay this stuff a bit to build better instruments.
Also, reread my previous post.