Establishing and following a routine is key to a successful training program. Constantly introducing new workouts with complicated instructions is not helpful, and can result in poor execution and sub-optimal results. Doing the same workout at the same time and place, week after week, is a great way to monitor progress.
This is not to say that week sixteen should look exactly like week one. As you improve, the target intensity should increase. Zone two is still zone two, it just starts a little higher. As your endurance improves, the time in zone should increase, especially for long days.
Another thing that should change during the course of a long training period is training zone priority, or dose, meaning which type of workout is emphasized. For example, aerobic capacity intervals are always hard, but they should not be done at the same dose all year. Early in the season you may want to emphasize aerobic threshold work, and do just enough aerobic capacity to keep the engine ticking over. Say, 10 x 0:30 with equal length recoveries. Later the spotlight will shift to raising FTP, so those workouts get a high dose while aerobic capacity goes up to medium dose, say 6 x 1:30. Later in the season you may want to push the upper end a bit harder and do aerobic capacity at high dose, say 5 x 2:30. Everything else about these workouts remains the same. Do them on the same day, at the same time. Same warmup and cooldown. Build a routine.
The training methods for swimming, cycling, and running developed independently. Each has its own way of describing workouts. For triathlon training, I find it helpful to approach them all with the same nomenclature and design principles. A lactate threshold workout should look about the same whether it is to be performed in the water, on the bike, or running. Cyclists often specify duration by time, while runners prefer distance - bike two hours, run twelve miles. I find it best to specify everything by time, because duration x intensity = work performed, regardless of how far you went.
Don't be tempted to try every new workout you come across. Too often a snazzy sounding, complex workout is more about a coach showing off their so-called skills. Keep it simple and routine.
Coach Gary