Firstly I do not do helmets
Secondly, I am too slow to complete them in time.
Yet I can sail through 200k Audaxes (or could a few years ago).
I often find that there is a clique of riders on an Audax who shoot off like racers at the start and are completely unaware of the slower brigades who tour around the Audax. The only contact is at the start line and that is soon forgotten about.
It is not unknown for members of that clique to "pack"* an Audax rather than ride around with the "value for money" (as they are derisively referred to) brigade.
As the min speed for an Audax is 9mph or even 7.5mph and the min speed for a Sportive is around 12.5mph, I dont quite see how Sportives are on the whole slower.
I notice that inexperienced is equated to being slow.

My speed is going down but my experience level is still going up.
*The term for giving up and not completing the ride.