Perhaps this can be solved with a few simple question:
Did the rate quoted in the original post of 10% apply to during a gnome event weekend or not? Does the rate of Epic Vault Keys during a vault event weekend increase at a rate proportional to the increase of normal vault key drops?
I noticed every response so far has said “as intended” while conspicuously withholding exactly how much “intended” is. You already gave out a rate with the patch notes, even though it is thrown out as a rough number that is in proportion to another number that was never officially stated, it is that ratio that does not align with data (which is why there are claims of it being “wrong” rather than just “too rare”), being off by a large rate on the relative scale over a large number of samples.
See also:
Which is far less anecdotal than people throwing around “I got one” versus “I didn’t” in this thread. Can provide math if necessary.