Ok, maybe I’m missing your goals or you need to provide a bit more detail. What are your group rides like now? What are the A rides like? Have you tried riding with them already?
In my experience group rides with “the A’s” generally tend to be long durations (say 2 hours) at a high pace (22-25 mph). Depending on your local terrain, there are usually a few sprint points along the way, maybe a city limits sign or a small climb (2-3 mins). These group rides are usually pretty forgiving for the sprints with slow rolling and regrouping afterward, but fairly unforgiving for people that can’t sustain the general pace of the group over the duration. So, the groups normally start off with a certain number of riders, but attrition along the way for those without sufficient aerobic fitness and muscle endurance. This is my experience, yours might be different, however your statement here suggests I might be close:
If you look at the plans, this is exactly what you are developing. The ability to put out more power over a longer duration. When you can do this with the A group and still have something left, that’s when you can think about trying to stick with the sprints when they happen. If you don’t have the foundation in place (bigger FTP), there’s really not as much point in building VO2Max. FTP is likely lower hanging fruit that will lift all your capabilities.