If like me, one has the time and recovery to train on the bike an average of ~10 hours/week then it's still the same problem: you'd be substituting training to run for training to cycle. And they are not the same thing. If they were, tri would be no thing.

I used to run many years ago when I didn't cycle. But more years ago than that, when I cycled a lot, I didn't run. Both running and cycling helped my skiing, but not running for 50 years certainly hasn't hurt my cycling. The group I ride with picks up newbies all the time: broken runners who now only cycle. I don't hear of running groups picking up broken cyclists. Certainly the broken runners are in better aerobic condition that if they hadn't been running but it does take them a while to come into cycling form, no matter how many marathons they've run.

Back in the day when I raced Nordic, there was a talented XC runner who was so frustrated with me because he knew he'd whup my butt on foot, but couldn't stay with me on skis. It takes time to turn talent and conditioning into ability in another sport. And once you've done that, you'll be worse in your original sport.

So yeah, if you want to really ride, then ride. If you're not that taken with riding, then also do any other athletics you feel like doing.

I have a license to fly, but payment is on the installment plan, the payments are steep, and only one currency seems to be acceptable.