I'm not up on PADI's current requirements for DM certification. A distance swim without equipment use to be part of this program. If this is the case, must this be accomplished in confined water? If not, perhaps this was the reason for such the exercise...
I'm not sure what PADI's requirement is ... but I doubt it's 800 yards in open water without equipment. As I pointed out a couple days ago, NAUI's swim test for dive pro, which occurs at the Assistant Instructor level, is 450 yards with no gear in confined water, and 900 yards with MFS in both confined and open water. The former has to be done in 10 minutes or less, and the latter has an 18 minute time limit.
There is a practical purpose to both of those exercises, both in terms of demonstrating watermanship and physical fitness.
I don't see a practical purpose to a no-gear open water swim for scuba divers ... which is probably why it's not a requirement.
In any case, I'm not sure how a dive professional's course requirements pertain to the topic of this thread, which was to discuss the benefits of increased requirements at the OW level.
I agree with your premise that a more stringent OW class would be beneficial. The question is how much more stringent is appropriate. Making a class hard just for the sake of saying you teach a hard class seems to me to be counterproductive. I want to turn out divers who are competent at scuba diving ... and while there is value in watermanship exercises, particularly in terms of demonstrating an appropriate level of fitness and in-water comfort, excessive swimming tests only serve to exclude people who are perfectly capable of learning and participating in scuba diving at the recreational level. I don't see the value in that.
As I said in an earlier reply, I think the test I took during my YMCA class ... 200 yard swim to get into the class and 300 yard swim to complete it ... was appropriate. I was even happy with NAUI's old standard of 200 yards, confined water, at the OW level. I think that's adequate for the typical scuba diver. I personally think NAUI's current standard of "at least 15 continuous stroke cycles", if applied minimally, is adequate to demonstrate that someone won't drown in a pool, but does little to demonstrate either competence or confidence in someone's in-water abilities or their overall physical fitness to dive. So I require my students to do the 200 yards ... which adheres to the standard and satisfies me that they'll be physically competent to perform as scuba divers in our local environment. Anything beyond that is, to my concern, overkill at the OW level.
... Bob (Grateful Diver)