I cannot speak for any but myself. I learned to dive before there were BCs. I never liked having anything around my chest or slipping and sliding all over me. I for a while used the horsecollar type BC (or none) until into the mid 70s when early wings became available and I have since never dove anything but a wing/BP. I have only tried vests and back inflates etc a few times and I HATE them with their cumberbunds and chest straps and plastic buckles and all sorts of doodads and I loath the way they slip and slide. They also fight good trim and usually require more weight which also fights good trim.
While I don't think a wing/BP is vintage a BP with Hog harness is as simple as it gets and is very traditional. A wing like my Mach V (18 and 30) with a simple Hog harness feels like I have nothing on me, it trims neutral easily and horizontal naturally, it is secure and stable and comfortable and there is no drag or rolling as with the potato sack with arm holes type BC that is so popular.
Luis, a wing/BP has less drag, it is not a rumor, you only have to try them in current to see. Not all are created equal, some like my old Sea Tec wing would luff and taco, my new Mach V units do not. They are tucked in so tight they ride in the slipstream/shadow of the divers body. There is nothing on the chest or shoulder flapping in the breeze, billowing pockets full of sand to grab the current, multiple D rings loaded with trinkets clinking and clanging. Luis, I see you have a new rig, you are headed my way, I see a convert in the making. You got the wing, now you just need to take the logical step back to a simple harness and you will be good as gold and you will feel just like you were in the 60s.
As well, a wing does not work like the typical jacket, a wing concentrates lift closer to the hips whereas a jacket has it up around the shoulders and upper chest, wings have by their design ZERO lift at the shoulders which is why they trim so nicely.
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I think that you are still thinking of the old Scubapro jacket from the 70’s with arm holes and buoyancy all around.
My vest has no lift on the shoulders and it does have the same 5 point harness similar to a vintage Sea Hunt style harness (I do not like cummerbunds either). It came with the same type of backpack I used in the 70’s (I did modified the harness to fully use the back pack strap slots). If you ever have a chance to try my vest, you will see that it is at least as secure as the best harness (possibly better, I would have to show you).
In my vest there is also nothing in front of me other than the same type of harness as in any backpack or even similar to a vintage rig. The only added flotation is on my sides down by my waist (nothing high near my arms). This extra floatation never has any air unless I am on the surface seating very high. Underwater the buoyancy is in the same location as a wing, but it is not allowed to form a taco around the tank because it is controlled by the straps in the harness. It is kept fairly snug against my body. You need to try it someday.
For doubles I am now using a horse shoe wing from Zeagle (will post pictures later) with no back-plate, just a 5 point harness similar to a modified vintage or any modern 5 point harness. I don’t see any advantage on putting a plate on doubles…they are naturally comfortable.
About the hydrodynamic drag, the answer is that I have tried it and with out instrumentation I challenge anyone who tries to tell that they can feel a difference. Human perception is so biased that it is meaningless in measurements of this type. On the other hand, instrumented testing at relatively higher speeds (like behind a scooter) have shown that wings can have a large amount of drag. Granted, not all wings are created equal, but not all vests are created equal either (lets compare apples and apples).
BTW, the lowest drag shown in tests came from using a Fenzy.
I agree that there are probably many poor fitting vests being used by many, but again that is just poor selection. There are also many that are way too complicated with weight integration, etc., etc.
There are definitely pros and cons to every type of floatation device I have ever used, but one thing in common is that there is IMHO some poorly designed equipment in all categories as well as some well design equipment.