I do both and have done both for a long time. I started as a runner who did a bike ride every so often. Then as I go older past 45 I started riding more because I enjoy it and it is different. I burn about 110 calories a mile running and speed is not so important because you are moving the same weight the same distance. The faster you go you just cover more territory in same time.
On a bike is it hard to make anything quite the same. Generally moving at 16-17 MPH on flat surface maybe burning up 25-30 calories a mile. Now start climbing or bring the speed up then the calories go up.

If I ride really hard I feel about 4 miles cycling is 1 mile running, but it is still different. If I do easy on the bike then more like 5 miles. If I run hard for an hour about 6 miles for me these days that would take more out of me than cycling for 2 hours. Running tires me out different that cycling and I think because it does not take the time that cycling does. I rode 54 miles today in 3 hours. That makes be tired but not the same way a hard 5-6 mile run does. For some reason I can recover from running quicker unless I am only riding for 20 or so miles.
bei
My real issue is that over the years my training pace in running has really gone down fast. If I do both running and cycling I cannot run faster than 10-11 minute miles. That seems pretty poor but at one time I was a 39 minute 10k runner. I fully believe that cycling a lot will destroy your running form and speed but running has injury issues and I use cycling to keep active. It is pretty easy to get injured running and cycling generally allows more room for injury, except for of course crashing and serious stuff that can happen on a bike.

I look at this way. In my best days I could run 10 miles training in 75-80 minutes and there is nothing quite like a good hard run when you feel good and fresh. However the thrill of descending at maybe 40 mph will never happen running and climb cat 1-2 climb and you will be gasping for air unlike running.