Lubricity is not the only parameter diesel fuel needs to comply with. Companies like Power Service apparently test their additives on many single fuel samples to see if their additives comply with these. Most additive aficionados don't look at the other parameters much and don't even think/imagine that putting stuff in would/might cause any harm. Its good that you guys at least are thinking about it and discussing it rationally.
The only thing that counts is whether the stuff actually improves something that matters, such as prolonging engine life or preventing a problem, and this at a reasonable cost. This can only happen if its used in a controlled comparison study in "real life" conditions. This has never been done and no additive manufacturer has ever published such a study.
What remains is that additives are still as originally designed: for specific engine or fuel problems. Usefulness as general prevention is a reasonable possibility that has unfortunately never been recommended by any manufacturer or shown by data from any fleet operator. If this were not true, such information would be all over the pro-additive message boards.