Agree with time constraints for training for all three disciplines totally, fitting in a run IS way easier than other stuff - sometimes. But as I get 'whisper whisper' a bit older, I am more aware of just trying to keep myself injury free ... I KNOW that cycling can massively help with run training, and for me, up here, swimming is a good alternative when there is a blizzard blowing outside and even the beach is covered in ice!! I can't do more than half a length of front-crawl without drowning, it hysterical to watch, but practise practise!
As for bike vs ability, I actually think that if you are a strong runner, you are likely to be a good cyclist anyway (similar muscles) so being cr*p at swimming is the least of your worries ... you can make up a lot more time on a decent bike and run than you can on a decent swim. Anyway, just saying!
I LOVE my mountains and running, they are my great passions, but variety is the spice of life ...
and of course, back to ULTRA RUNNING ... of course ... for all those that live miles away from Centurion Races ... I have my finger nowhere near the NDW race button! I have, however, saved all my relevant ultra racing history in a word doc so I can transfer it over to my WHW Race entry - oh boy WHAT a complicated entry process!