Actually I have attached straps to 3 different NLs. That's not a large enough sample, perhaps. However, they were all tighter than the FP El, but not all that different from each other. I am 77 years old without the grip strength I used to have. Yet, with the right grip, I did it. With the wrong grip, I couldn't.
As far as a Swarovski dealer struggling to attach the strap is not surprising. How many of them would even bother to first read the instructions, when they are supposed to know it all?