Bottom line is that it is up to you to understand the culture of the group ride and adapt to it, rather than the other way way around. Many ride descriptions on websites haven't been changed since they were created, were probably overly optimistic to begin with (e.g., we will have three different groups, with assigned leaders), and the nature of the ride has evolved over time. The only way to know what is going on is to do the ride and to talk to the regulars.