I disagree with OP. Cycling, in general for me, is much more fun than running if I isolate the experiences to just themselves.
You get it all:
- More terrain
- More vert
- Adrenaline rush coming down the mountain
- It's an adventure
I used to be a serious, consistent runner until about 2-3 years ago. In my most dense training I would stacking 4-6 weeks around 95-105 a week, two+ workouts, long run, etc. I could reliably hit everything from 3:50 1500s on the short end to 1:06 Half Marathons on the longer side and with consistency. I took it seriously and I loved running.
I stopped running seriously because as I got to 30, I realized PR opportunities would slip away because I no longer wanted to devote the time and energy to that sort of training while having a family, focusing on career, etc.
I still loved running, but trail runs didn't quite scratch that itch. I live in the mountains and realized that I can find the magic with more exploratory adventure sports. Skiing and Cycling more than fill that. There is something about going for a 4-5 hour ride and doing 45-60 minute climbs as you go up in altitude that can turn any ride into an intense workout, but then you get the adrenaline rush of bombing down a mountain. Skiing same. Resort is fun, but hiking or skinning up a mountain for 1-3 hours and then hitting a long run can be just incredibly more fun than a run, and still exhausting.
The difference is a 4-5 hour ride you may get 1.5-2 hours of genuinely hard work (2-3, 40-45 minute climbs but then lots of flat cruising and downhill adrenaline.
Skiing? Same thing. Go hike up a mountain for a couple hours with your gear on. You'll get your hear rate going, see beautiful terrain, be outside and of course get the rush of that downhill that racing will never ever be able to grasp. (Except for the rush of competition in a tight race where you are in the mix to win).
You can match that rush of competition on any ride or ski you want. That's why it's better.