That happened to me soon after I started cycling slightly longer distances, when I was still riding my hybrid. It was with a local group and they soon left me behind, but none of them was brave (or kind) enough to actually say to me, look maybe this isn't the ride for you just yet. They did wait for me now and again, but with rather bad grace. It was a very dispiriting experience, and even though I could keep up with them easily now I wouldn't want to cycle with such an unfriendly lot.
As you know, we are not the type of people who would be so ungracious or friendly about something like that. We would change the ride to suit.
Maybe we should invent a CC speed scale: Pootle, Bimble, Touring, Brisk, Speedy, Superspeedy, Chaingang?
This is a jolly good idea