This. One thing, your bike handling won't improve when you run. And most people who came to cycling from another sport (your truly included), start with some very bad techniques that can really bite you in a race.

You can excel as a triathlete (rather, being slightly above mediocre in all three sports) or excel in cycling, but not both.

Triathlon means you go at lactate threshold or slightly below for all three sports; cycling, especially crits, is nothing but a huge minute on, minute off interval.