A structured training plan, like TrainerRoad's triathlon program, can indeed benefit a cyclist solely focused on two wheels. While it does incorporate run and swim workouts, you can adapt it to your needs.
First, understand the philosophy behind the plan. It's designed to build endurance, power, and speed - all transferable to cycling. The brick workouts, while specific to triathlon, can be seen as intense cycling sessions followed by recovery rides, simulating the demands of long cycling events.
To adapt, simply replace the run and swim sessions with cycling ones of similar intensity and duration. Keep the structure and progression of the original plan, and you'll be reaping the benefits of structured training, tailored to your needs.
Remember, the road is a mysterious place, full of surprises and challenges. Adapt, overcome, and you'll find your legs carrying you further than you ever thought possible.