Here's my perspective. Some of the swimming might be out of date, but my experience is relevant.
I am/was not a strong swimmer at all. Always lived around water and enjoyed it, but not a good swimmer. I actually did pretty poorly on the first day of swimming 250 m timed test. Despite a horrid score, I was kept in swimming. Frankly, you have to be halfway drowning to do poor enough to be placed in basic swimming. For us, no one really regretted basic swimming. The disadvantage was that it was 16 lessons instead of 8 lessons, but they went from complete zero (blowing bubbles in the water to get comfortable, no kidding) to finishing the normal syllabus of non-basic swimming by the end. They typically got to do basic water survival instead of normal water survival, which was also a tad less stressful. I don't remember anyone regretting basic swimming at the time (2008).
My swimming experience was meh. We learned the different strokes, swam a couple 250 m (in 25 m segments) a class, and practiced the strokes. The pool was frigid, that was the most uncomfortable thing for me. The 1 mile swim wasn't pleasant - I am NOT a long distance swimmer! I took a while, but it wasn't the end of the world, no worse that a hard run. They let us jump off the platforms during class if we wanted (I never did). Goggles are allowed
I was really dreading water survival. Like, a lot. I stressed about taking it for a long time. After doing it, I had nothing to worry about. For one, I was much warmer wearing BDU (I'm old....) pants and blouse. We practiced survival swimming stuff. We had to float for 20-30 minutes on our bellies. This entailed holding your breathe while floating and then lifting your head to take a breath when you needed it. I didn't think it would be pleasant but it really wasn't that bad. I just relaxed, ran a movie in my head, and did the trained movements. No biggie. Treading water was more challenging as I wasn't particularly good at the egg beater. I probably looked like a drowning dog, but go through it. My instructor had to yell at me to relax - I was fine after I took her advice! We had to try and swim 25 m with BDUs on underwater with one breath. I actually wasn't able to do that at the time, but the downgrade was minimal. We did a jump from the 5 meter platform and several from the 3 m. I'm afraid of heights but the 3 m didn't bother me and the 5 meter was only a minor inconvenience. We were always given the chance to do the 10, but I didn't (that fear of heights). Lots of people did and loved it. On the last day during the final exam, I finally did the 10 m once and only once. It was no where near as bad as I thought and I did fine. You jump, swim under the bulkhead (about 4 feet), surface and clear.
My greatest confidence boost was on the endurance swim. We are given 20 minutes to do laps in the pool with 50 m increments. Max score was to do 16 laps (800 meters). I was in the normal class - so there were many more swimmers who were more confident and better than I was. I struggled in the swim class doing the mile swim and was concerned. Unlike swim class, we had to keep either the pants or blouse on for the swim. I kept my blouse. There was a big difference that helped me. We were told to use freestyle (the 'crawl') in normal swimming, but we could do anything for the endurance swim. I did a modified elementary survival backstroke (or whatever it was called). I managed to finish first and in only 16 minutes and I was not out of breath. Let me tell you, that made me feel good about myself!
I ended up with a B in swimming and an A- in water survival.
So, practice if you want to, but also don't get worked up about it. The curriculum may have changed somewhat in the last few years. However, I doubt it has changed much and after taking the classes, I was certainly way more concerned than I needed to be.