My progression was running -> mountain biking -> triathlon -> ultra marathons -> road bike racing.
Generalizations:
For both runners and roadies, the best of the lot are mellow and appreciative of their talents, and willing to help others, including clueless new comers. The second tier - the ones that have some talent and are good and can win a race if the top dogs don't show up - can be uptight arrogant PITAs. But overall, roadies are the most uptight, self-centered and cliquish group of all these athletes I've ever met.
I did triathlons back before they were the big business they are now. And what a business they are. A 1/2 IM I did in 2000 for $100 now costs over $400. The first time I did it, I signed up on a whim two or three months before the race, but now you have to sign up within mSec of the opening of registration 9 months before the actual race. Now that I'm older, my wave usually goes at the end, which means that I have hundreds, or even thousands of cyclists riding all over the road in front of me that I have to wade through. The young studs that are faster than me on the bike started their bike leg long before me, so I've got tons of MOPs and BOPs from their AGs littering the road. No thanks. Give me a small, no-name race with 100 experienced triathletes any day. Plus now the charities are involved (I am not going to contribute to a charity just so someone can do a triathlon in Florida). Triathletes do have an odd streak to them, whether it is the underwear run or whatever. As far as the MOPers sending their power files to coaches -- I know plenty of roadies who do that, so that sure isn't limited to triathletes.
The MTB scene in the 90s was cool. Mellow vibe. Race hard, crash hard, get muddy, tailgate in the grass field afterwards. Ultras are like that too. Their races are the simplest: do or do not, pure and simple. Fat asses should be the model for other events. However, they have an odd dichotomy of claiming to be low-key and supposedly eschewing bragging, yet they wear their race t-shirts as badges of honor at every running event.