It’s amazing how a few years of really sticking at swimming can transform your performance. There are sometimes breakthroughs but most often it’s a hardly noticeable week-on-week improvement. Similar to watching your run/bike training times gradually drop over a similar time frame.
Of course many of us don’t focus on run and bike technique as much as we might. For those times drop because of both technique and fitness. In the case of swimming technique plays a bigger role.
Although for all three technique will be a limiter to how far you progress. And then when you try to change it and put all the power/fitness into a new technique watch out for the injuries. Best to work on technique every week in all disciplines I reckon.
IMHO for run/bike small amounts of speedwork with higher cadences is the most easily effective.