This is the standard view for me when riding with the full-time cyclists.
You are a triathlete. That means you train for three sports simultaneously. You are (as one of my friends once put it) striving to be solidly mediocre in three sports. That means that when you pit yourself up against dedicated swimmers, focused cyclists, and well-trained runners, you are probably going to come up short. Why? Because you're not trying to be the best swimmer, biker, or runner; you're trying to be the best triathlete.
But when the triathlon season is over, there's no reason to continue to pursue adequate mediocrity in three sports at once. Why not focus on just one sport, and get really, really good at it? What if you can make your "solidly mediocre" as good as a single-sport athletes' top performance?
It was this step, more than any other, that brought me more success as a multisport athlete. Running was always my weakness. I didn't like it; I didn't want to do it; it was my primary limiter in every race I did.
But I signed up for a half marathon anyway. And then I did another one. And somewhere in that training to go long, I encountered a runner within myself that I didn't know existed. I started to enjoy running, to look forward to it, to consider myself a runner. Of course, once the triathlon season came back around, I became (once again) a triathlete. But the hard work I'd put in and the improvement I'd seen stuck around, and by this season, I was running 8:30/mile instead of 9:20.
My guess is that for most triathletes who weren't previously athletic, running is the limiter. If you came from a running or cycling background, swimming is probably your biggest struggle. If cycling is your weakness, that's completely legitimate, too. Whatever your weakest sport is, you need to figure that out (I bet you already know it, if you think about it). My recommendation to you is that you do an end-of-season focus on that sport.
The alternative to choosing your weakness is to choose what you like. You probably won't see as much benefit going into next season, as far as catching up to your competition, but you will still come back stronger, more capable, and more confident in your abilities. Last year, I focused on a half marathon at the end of the season, and it saw my average speed drop by 50-60 seconds per mile; this season, I'm focusing on cyclocross and group riding, and I think by the end of next season, I can easily be averaging 22 MPH. That's not going to provide as...