Cyclists who ride faster tend to favor tight-fitting clothing because loose clothing creates a lot of aerodynamic drag. The drag goes up as the square of the velocity, so a mountain biker on a singletrack climb might wear baggie shorts, but it behooves a road cyclist that maintains over 30mph to wear a tight-fitting merino jersey or lycra rather than anything that will act like a drag chute. Close-fitting clothes make it difficult to conceal a firearm within the clothing. Open carry is legal in Colorado except in Denver, but it isn't advisable. If you can't conceal it within your clothes, your choices may be to have it in a backpack, waist-pack, or chest bag or on a bag that's mounted on the bike.
Cycle tourists and bikepackers have the opportunity to take the weight off their body and put it on the bike, but a handgun is one thing that may be preferable to keep on one's person rather than on their bike for the same reasons it's preferable to have it in a holster rather than in the car or a handbag. A body-mounted bag like a backpack may therefore be preferable to a bike-mounted handlebar bag, saddle bag, frame bag, or pannier.
Paul Harrell has recommended his Five-Seven for cycle-touring at least a couple times because of its low weight. I think it's his solution looking for a problem and I've not heard him ever claim to have cycle toured or even ridden a bike instead of driving one of his classic muscle cars.
Riding on the road can be intimidating in our car-centric culture where
women and little children get bumped-off with possibly not even a legal consequence to the driver. Nevertheless, bicycling is still statistically safer than driving a car. Want to wear a helmet? Use it in your car where you're far more likely to sustain a head injury, but use it on the bike too because they work. But don't be afraid to ride on the road because the roads weren't built for cars and they don't belong to motor vehicle drivers.