I'm sorry that you had a bad experience with these leaders. Here are a few tips that might help you in the future:
1. Tying stronger knots. As the community has already stated, all knots weaken your line, and some are worse than others. I've attached an image of the Fly Fisherman test referenced earlier - and both a clinch knot and Palomar knot would both fail your "5lb" test.
I would recommend you use the Trilene knot, which is fast and easy to tie, even on small flies. You should also be sure to wet the line before you tie so that it slides well.
2. Avoid bug spray when handling monofilament. Even oils used in Burt's can severely damage plastics: Essential oil - Wikipedia, the free encyclopedia
We're a full-service fly shop, with loads of expertise in the field. In the future, it would behoove you to actually
contact us via e-mail or phone if you have any problems, rather than posting about it online. Please feel free to reach out to us at 888-413-5211, and we'll happily help you through your issues.
We are an authorized dealer for Rio, and I can assure you with 100% certainty, that if we couldn't sell 4x leaders faster than the monofilament degraded, we would not be in business. The leaders you purchased sat on the shelf, inside an air conditioned facility, for no longer than a few weeks.
For the rest of the community's benefit, the OP's order was placed on July 12th, shipped on July 12th, and arrived on July 14th - which was in fact about a week EARLIER
than was promised.
Trident Fly Fishing