Swinley is busy and continues to get busier, that’s the downside of cycling becoming more popular; the area being regarded as great riding for the south-east and it sitting in a heavily populated part of the country. It will continue to get ‘worse’ for volumes of riders in my opinion, even with the changes to the ticket/car-parking situation.
The BoB ride on Saturday was an ‘intro’ ride for prospective members, so the speed and capability is probably lower than a normal group outing. Rightly or wrongly, these are often quite large groups, but they are there to show people the trails that BoB worked hard to build and continue to develop and maintain.
As mentioned above, there are plenty of other trails to ride, and 7 mins for 25 people to pass seems an infeasibly large time where you couldn’t make any progress, or turn around and follow them off that trail.