Given that you can machine/hammer swage an entire shroud for the cost of one stalok fitting, and given that machine swages have worked for a few decades, it's hard to argue that it's unwise to use them.
And when you're on the receiving end of a mast toppling towards the water, on a 12 year old vessel in well off shore in the fall on the cold and stormy Northern Atlantic, you might think other wise. Lower swage failure, wire was still fine, mast furler and sails were all toast and had to be cut away to save the vessel.
In the NE we get temperature cycling which when water gets into a swage can cause it to freeze and eventually split and/or crack. I've seen lots of cracked or split lower swages. I have four stays in my shop right now where three of the four lowers are split but the wire is still serviceable.
I think, in the end, we really are lucky that we have a number of good options.
Which one is best? Frankly, all modern 'good' swage options outlast the wire they are attached to.
Please, if you are going to state something as a fact, to prove your point, the least you can do BACK THE FACTS UP WITH THE EVIDENCE or don't state them as factual. I for one would love to see some data on this because it has not been my experience here in the NE. It is out of line with what myself, or the four riggers I am friends with, see here in the NE and why none of them want to install swages on the bottom unless specifically asked to. Their preference, based on real world experience, here in the NE, is mechanical on the bottom swage on top.
So it seems to me that simply picking the one that feels good and running with it makes sense.
I guess it all depends where you sail and what you've seen and whom you've spent time talking with. For me I will never again use swages on the deck end of a stay in the NE. Been there done it seen and experienced my own failures. Even being the weakest mechanical fitting I have yet to seen a Norseman fail though I am sure some have. OTOH I have seen LOTS of swage failures. My rigger has seen one failure of a mechanical fitting but it was due to installer error.
One last thought... inspecting the fittings every month does way more for security than spending a ton of money on 'bullet proof' fittings and never looking at them again...
So you have a dye kit to catch these weaknesses at their earliest? I agree 100% that visual inspection is good to do, but you'll never see it all. The boat I was delivering had JUST gone through a complete rigging survey and showed no signs of failure until the mast went overboard..
Outlast the wire, maybe, maybe not..
If I was in an area where it never froze then I would probably consider swages on the lower end but not up here. Once you personally experience the loss of a stick due to a swage fitting failure you begin to consider all other options. I have been using mechanical fittings since 1991 and still re-rig every ten years and I don't re-use them..