It is interesting to note that Sun Yang, when he set the 1500 meter world record in July, did so holding an average of 58 seconds per 100m for the entire race, using a 2-beat kick for all of it except the last 50 meters or so. 15 consecutive 58 second 100 sprints! We may consider that there may be more long-term benefit by developing a whole-body synchronized stroke with 2-beat and using that skill to get down to a much faster pace before falling back on the much higher energy consumption (and drag increasing) 6-beat kick.
When analyzing elite swimmers swimming a certain style stroke (and kick) at world-record pace, that may not be the best role model for a stroke aiming for a slower pace. In a blog essay I argued once that we might consider learning to swim slow like Phelps before we try to swim fast like Phelps (or name your favorite swimmer). The forces of water opposing a swimmer at 48 second pace are far greater than at 60 second pace, or 80, etc. The water pressure in front increases, the body is lifted to a higher plane in the water and other changes affect the effectiveness of the stroke. Therefore the stroke choreography and power application need to be adjusted accordingly.
6-beat kick is very powerful, when complementing a well-designed stroke, rather than covering up its weaknesses, or worse, working against it.
PS- listen carefully to the comments made by the commentators on that video clip of Sun Yang. They are acknowledging how ‘slow’ and relaxed he looks while clearly crushing the competitors- how misleading his appearance is. It is the classic misconception of TI- a beautiful but slow stroke! They might think that until they actually try to swim along side a well-developed TI swimmer.