a. I'm not sure we've explained why the thread modulus needs to match the rope
modulus. Could be true, but I've not seen a provable explanation. I can lace a tramp to a rigid boat or tie myself to unyielding rock with nylon. In fact, the nylon will have a greater ability to self-equalize, like a lacing. By the way, I've always found high mod line on tramp lacing to be pretty silly--the wrong material for the application.
b. I've broken ~ 50 samples over the last few months--line and webbing--and I have NEVER seen variation beyond 15%, high to low within a given material combination. Most of that variation was due to changes in stitch count (I presume some samples with fewer stitches had less uniformity). These were all hand sewn, and though I may be experienced, I'm not an obsessive craftsman.
c. They don't zipper. In fact, I've cut threads at full load intentionally to reduce strength. At most the efficiency drops 10-20% if the count is sufficient.
d. The scissors analogy makes no sense, the bends are not that sharp in proportion to the thread; if you see the thread pattern under load, it is more like a lacing.
e. There is plenty of area on line; I've broken lines up to 5000 pounds with only 2 inches of stitching.
f. I've seen no evidence that box stitching is magic. I think there are certain practical matters; it gives a peal resisting row at all edges and it is simple. But climbing gear
is all bar tacked. I'd be happy to look at the numbers, but my testing indicates that a number of cross rows is more efficient.
g. Once zippering starts, there is no pattern that will resist it; it's fast. Better, figure out where it is starting and stop it.
h. Machine stitching depends on even tension because it is inherently unable to adjust to the load (interlocking loops). On short runs I can see that this is a challenge. Bar tack machines do not suffer from this because of the high thread count (that last is a guess).
i. Whipping twine will generally be more UV resistant than fine thread, but in any event, stitching will require protection. I can think of many proven methods.
j. Tenera thread, to my knowledge, is limited to 19#. Even after 5-8 years, plain 50# nylon twine will hold 20 #, and portions out of the sun far more. Great for awnings, but not very interesting for high load applications, IMHO. And there are heavier twines (#8 is ~ 100#) for larger lines.
Opinions, generally backed by testing. But I'd love to see more data. I'm sure I can learn more.