I usually try and run with another person even if they are slower because I find it less monotonous. Nonetheless in the dozen + runs I’ve done so far almost everyone takes off after mile 1-2 at a pretty fast clip (for me right now) of around 7:30 mile pace, even when in C group the other day. I kind of understand that because there aren’t many people out there yet so you join where someone is, today I plan to do a 5k in the “D” group simply because it seems to have the most people signing on (I think the other group had none last time I checked).
I did notice the Zwift comment on social runs and will stick with the pace group if there is one.