Just an observation, the last summer camp that I lifeguarded for the BSA required all scouts to pass a "swimmer" test to be allowed in the deep end and to be allowed on boats, canoes, etc. This included floating for 2 min unassisted and swimming 200 meters. IMHO anyone with somewhat basic swimming ability can accomplish these requirements.
Should it be a requirement for SCUBA...? I'm not one to make that decision, but there is definitely a benefit to having the ability to swim, especially in a safety sense.
I am not sure I understand your point here. I don't know of any dive certification agency that does not already have swimming requirements that exceed this.