All swimmers reach a point where they are not going to get faster unless they address the technical flaws in their stroke. The only question is the potential benefit of those changes. For Michael Phelps, he's technically proficient enough that fitness will do more for him than technical changes. He could certainly go faster if at peak fitness, he made a few technical improvements. But obviously, faster for him is not going to be minutes or in some cases, won't even be more than 1 second.
Conversely, most triathletes are simply poorly skilled swimmers. And many will claim they want to improve their swimming, but are scared to try anything different, as though it might be wrong, or that they will possibly get slower. Problem is, if you're not willing to take that risk, you're already proving you'll never get faster. Fitness isn't the problem for most triathletes, (look at how much they can run and bike!) Skill is the problem. If you won't give an honest and committed attempt at fixing the skill, which requires experimentation, you're wasting time you should spend biking and running.
This week I have been in Tenerife, Canary Islands, and it's been great to work with a group that was willing to risk swimming slower. A few of them did, at first, but by week's end now, they are all swimming faster and with less effort than ever.
I will be speaking and doing underwater video analysis for athletes and coaches in London, at Hampton pool, this Sunday. I will discuss the 3 key items for improving swimming. If you're in the area, or know someone who might benefit, details are available at www.tridynamic.co.uk.
If you can't make the talk, but want to learn more, check out my swim webinars at Performance Webinars.