Threads stripped out sounds like wear and tear, not defect.
Did you wire wheel the heck out of them and apply lubricant before adjusting? - self induced.
Did you have adequate thread engagement? - self induced.
Did you torque the jam nut and use locktite to hold it fast and prevent wallowing? -self induced.
I would imagine cracked welds would be the only thing they would warranty long term based on the typical use of a lift kit on a jeep. I don't know the details of the RC warranty, but if it isn't a "what ever happens, even if it's from abuse" warranty you're probably stuck. Cost for adjustable arms is not the worst, or move up to a bomb proof warranty type vendor with a reputation for better parts. That's gonna be much more than 95 bucks.
Pro-rated your arms only cost you 19 bucks a year for the use you got out of them. I'll bet you won't wear the next ones out before the body turns to powder.
'00 XJ - Somewhat modified
'01 Venture - high mileage, paid for, shut it