I think it'd be fine without Iain, most of his jokes are either really obvious or really old ones he's used before, plenty of good comedians out there who would add something to the show. I agree that previous series he was part of what made it fun to watch, but it just hasn't seemed to work this one.
Watching some of the old challenges back on YouTube from older series and they were so fun. Some were a bit brutal, but actually they usually talked them through after, and it didn't feel serious or heavy- they laughed along usually as well. There haven't been any good challenges this series imo, movie night was a good opportunity but what they showed was actually pretty spiteful and not overly entertaining in my view.