Obviously if you have wider responsibilities / are dealing with kids / are going out into the wilds then a different take on things is not unreasonable.
however for most of us riding with friends not far from civilisation then there really is little that a first aid kit makes a significant difference. Minor injuries carry on, major injuries call in the experts / self evacuate.
In between that is a small amount of injuries where having the kit and the skills to use it could make a difference between continuing the ride and not or significantly alter outcomes/ comfort for the more serious injury.
Significant gravel rash say – can be much more comfortable under the right sort of dressing or being able to steristrip a cut up. Having the kit might mean you could carry on rather than cut the ride short. Once or twice I have done this sort of thing. However I don’t often carry a first aid kit although when I do its fairly comprehensive.
The only time I regret not having the kit is when a mate broke his shoulder – and then only because I could have offered him some of the very strong painkillers I have in it when we were on the hours drive back to Edinburgh with him.
It is interesting that those with skills in the medical world are the ones who don’t carry much first aid kit.