In my experience, every second matters in a sprint. I typically win or podium my AG, and frequently one of the positions from 1st to 4th were decided by fewer than 5 seconds. Any piece of gear that can make a second or two of difference is worth it.
Now in your case, a sleeved top is faster than a sleeveless. That alone could be a second or two in the swim. I bet more than a few. Then a one-piece will be a little faster overall than a 2-piece on the bike and in the swim. If you are aiming at the top of the podium, I would get a good, sleeved, one-piece tri suit.
That’s pretty much my experience too. (on a local level)