Weak links work harden with use, which results in a well used one having a higher breaking strain than a fresh one. Its not unusual to have a weak link last months, only to then have two or three break replacements in quick succession, until one survives long enough to get enough launches to also be work hardened.
The Air Cadets had a policy at one time of giving pilots a new weak link for a first solo flight, which was just about the worst thing that one could do, as it would fail at a lower tension than the cadet and winch driver was used to on the previous launches.
If a weak link of a particular "spec" can be so different in service as to break readily when new & not break after work hardening to the point where it is so noticeable then the spec must be a bit wide!
As for ripping the hook out, I was being a little flippant
that is more likely to happen to aged wooden a/c possibly suffering from woodworm.
The more likely scenario would be a hangup & I was a member when that happened although didn't actually see it. Winch driver franticly whacking at piano wire over a piece of railway sleeper with a 7lb axe, glider doing tight circuits with 3ton winch hanging underneath. I designd & built a giulotine that cured that problem but was never used in anger. No doubt things are safer today than in days of yore & clubs routinely change weak links regularly, but how many new ones does it take till you find a "good" one?
The fact that gigamilions of launches take place successfully only proves that the release mechanism is an excellent design & a weak link is not required because pilots are not trying to pull the wings off.