Agree, but we're talking about single tank rigs here, so "lots of deco" isn't a consideration. V-weights for doubles are still easy enough to find.
I prefer non-ditchable weight for three reasons:
1) I think it's safer
2) Comfort and mobility
3) Reduced risk of equipment loss
Comfort and mobility:
Non-ditchable weight can be tucked away where it is less likely to cause discomfort or restricted motion. A steel backplate, a heavier tank material, a weighted STA adapter, a P-weight, trim weights attached to the backplate, are all examples of places you can put weight that don't in any way interfere with my range of motion or take up valuable real-estate where I might want to put something that I actually want to access. In contrast, any weight that is in my hip area would rub on my hips uncomfortable, and would only get in the way of the D-rings on my waist where I may want to clip things, and would make tightening the waist strap more of a hassle. Any weight on the back of my belt would get in the way of the tank. If it was on my harness strap, it would make cinching it up more difficult, and if it was an external weight belt, it would only interfere with the harness strap (the buckles would be hitting each other..).
Safety:
Most forms of ditchable weight are highly prone to accidental dropping. For example, weight belts can easily slip off a compressed suit, or a weight belt buckle slightly bumped flies open, velcro in BCD vests may not hold well, etc. It's incredibly common for people to drop their weights, in fact most people have probably seen it happen. When the weights are dropped, chances are the person is going to have an uncontrolled ascent. On a deco dive that may cause DCS, but even on a rec dive the surprise of an uncontrolled ascent could cause a chain reaction of other things such as forgetting to breathe resulting in pulmonary embolism, or frantically grabbing onto a buddy and ripping the regulator out of their mouth, etc. An uncontrolled ascent is an out of control situation, and when the situation gets out of control other bad things become more likely. I would prefer that myself and my buddies minimize the risk of out of control situations.
As a new diver on one of my first club dives, I got paired up with a 20-year diving veteran to look out for me, and on our first dive he accidentally dropped his ditchable weights and no surprise he immediately went shooting up to the surface -- luckily I was paying attention, and was able to grab his weights as they fell in front of me with one hand and grab him in my other hand, then we did a very awkward dance as I tried to put the two back together.
Some will argue that carrying no ditchable weight creates different types of safety liabilities, and I've tried to listen to those arguments with an open mind, but I just don't see any logical merit to them. The most common argument I've heard in support of ditchable weight is related to complete incompetence or carelessness: what if you don't understand proper weighting and put WAY too much weight on, OR what if you forget to attach your LP hose to your wing, AND then you forget to test the inflator valve, AND then you forget to inflate your wing prior to jumping off the boat, AND none of your buddies/dive assistants notice before you jump in the water? Well, I'm sure that does happen, but in such a situation a person should simply unclip their belt and ditch the whole rig, which is probably not any slower than fiddling to remove weights from pockets. It's probably easier for your buddies to locate a complete rig than an individual weight anyway. In any case, such a scenario can be avoided by simply following basic dive safety protocols like knowing how much weight to carry, and checking your inflator and inflating your wing before jumping off. I don't think that it merits changing your gear configuration in a way that introduces an additional point of failure. The two are not equivalent, because proper adherence to protocol can avoid this type of error, whereas there is no protocol that you can follow to guarantee your ditchable weight won't accidentally drop itself when you accidentally bump a buckle or get a ripcord snagged on a line or something.
There are some situations for ditching weights I've heard other than complete incompetence/carelessness, but they seem to rely on extremely pathologically rare scenarios, and even in those pathological circumstances, it seems that ditchable weights are STILL not really needed. For example:
a) What if your drysuit springs a leak? Well then you can use your wing for extra buoyancy.
b) What if your drysuit springs a leak and you aren't using a wing? Even if it has a leak, it's not going to magically lose all it's buoyancy, most of the bouyancy will remain and you could probably orient your body to avoid losing much air at all, and you could also still add air to compensate for the leak
c) What if your wing fails to inflate on a wetsuit dive? Well, to avoid uncontrolled descent we usually add air as we descent to compensate for suit compression, so you should probably notice a failure within the first 20 feet which means you don't have much negative buoyancy yet and should still be able to swim up.
d) What if the wing inflator mechanism doesn't fail until you're already at depth? Well in that case, assuming you were adjusting buoyancy during your descent, you would already be neutrally buoyant when it fails (or close to it), which means it should be easy to swim up, and then the reduced pressure will inflate your BCD even more.
e) What if you made an uncontrolled descent and made no attempt to add air into the wing until you were at an extreme depth, and then found the inflator wasn't working? Just don't do that? But even if you do, then you can orally inflate your wing
I'm about out of ideas, and I still haven't thought of a situation where I'd need ditchable weights...but even if you think of a good one, you should be able to ditch the whole rig and get assistance from a buddy, or do a CESA if you're alone (no deco)..
