I think everyone should know how to swim, and am amazed at how many do not.
That said, I don't think swimming skills, as such, are used much in scuba, aside from a couple of the basic kicks. We don't use our arms for propulsion, and most of our education is in how to get down and up safely, not so much how to move horizontally. We tend to "swim" (meaning fin) very slowly, conserving air. In an adverse current, I try not to swim, but pull-and-glide along the bottom or the wreck, or the non-coral features of rocks.
BUT if things go wrong? We divers spend a lot of time on the water, and you may not have your gear on when an accident happens and you have to swim for it. Or you fall off a dock? Or you have to jump in and rescue someone? I also agree that knowing how to swim makes you more confident in the water generally.
Also, if you are not strong at just finning, and don't exercise those muscles when you're not diving, you may come to regret it on some dive when you just *have* to buck a head current to get to that line, or that distressed diver.
Anyway, at 62 I still get into the pool once a week for 1000 yards, and can do 250 yards comfortably in about 6 minutes on mixed strokes, 5 min if freestyle and I push it. I definitely need goggles/mask though so I can keep my head down. A mile takes me about 44 min on those rare occasions I do one.
Important thing is, do some of those laps with just a kickboard (no fins), those are your real diving muscles, keep them fit and they may save the rest of you some day.