The principal reason that breaststroke is slower than the other strokes is that so much is done the wrong way underwater. Breaststroke is the only stroke in which you recover your arms underwater. and is the only stroke that even has a kick recovery (which is also done underwater). You can, of course, recover your arms over the water if you're not bound by the rules of competition breaststroke. It used to be that the rules for compeititon breaststroke were looser than they are now, and that's what breaststrokers began doing. It got to the point where it appeared that the old way of doing breaststroke was going to disappear, and that's when they tightened the rules for breaststroke and began calling the breaststroke with the over-the-water recovery and dolphin kick butterfly.