A = resources you have to waste to attack the coin
B = market cap of the coin
k = constant
Y = Probability the coin is succesfully attacked in the real world = k * (B/A)
Since A in a POW coin is proportional to inflation rate you can conclude that as inflation goes down the probability of an attack increases.
History has shown that
B tends increase when inflation drops with Bitcoin. Perhaps it won't always do so in the future, but unless you are claiming to be psychic your comment concerning Bitcoin is ahistorical and fallacious.