It can be of poor design, yet still work. Just don't change it. Pack riding develops handling skills, provides experience with race dynamics, and makes the time go faster. But all too often, the group will cause you to ride fast when you would be b est served by a slow, easy recovery ride. At other times, you'll need to go longer or shorter than what the group decides to ride.
Group workouts too often degenerate into unstructured races at the most inopportune times.
For the winter base-building period, find a group that rides at a comfortable pace. During the spring intensity-building period, ride with a group that will challenge you to ride fast, just as when racing. Smart and structured group rides are hard to f ind. You may need to create your own. Stay away from big packs that take over the road and are unsafe.