I don't disagree with this at all, but the OP framed the question around retention versus tac reloads and not speed reloads. If a gun fight has gotten to the point that I am having to reload, the gun fight isn't going well...I'm fine with that so long as everyone on my team gets to perform an in-battery "speed" reload, because if time is a factor that is what I would teach and what I would do. Retaining the magazine is a very low order priority for me, and even moreso if I've got yet another full spare magazine on my belt even after reloading the gun.
That is a very reasonable statement when taken in that context. If the question is which is the fastest way to complete the initial reload, I think the timer would show going to a pocket is faster. If the question is having to retrieve the partial mag and perform a reload with it, that adds to the dynamic some. Would the faster storage method be negated by a slower secondary retrieval? Clothing styles and pocket contents would also have an impact on that as well.Conversely, I'd say if you can remember to retrieve the magazine from whichever pocket you put it in, in whichever orientation it's sitting, under stress, great.
The difference is that presumably I'm only performing the mag stowage when I'm in control and feel like I have the time/safety to do so, whereas I may need that spare magazine (wherever it is) under immediate life-or-death circumstances and the stress that goes with it.