Agreed.
In RotBP, I liked playing the mission on solo for the first time, to get to know it and the objective(s).
Here, you must play in public to learn a new mission, sometimes with beginners teammates, sometimes with a strong antagonist and this kind of thing.
And in RotBP, you could only get gold the once for each difficulty setting.
But being able to progress even when playing solo would be a great addition.