With out large sample size it literally might be bad luck. Remember you can also run the dungeons uncapped so they are significantly faster. Not saying that you might not be correct but again they might have went from 5% -> 25% and you still are just having bad luck. Each roll is essentially independent of each other most likely. It's possible to have a 50% drop rate and still not get the drop for days. Either way I guess you have to ask yourself whether an outdated weapon is worth the headache for the glamour/head start on the next relic (if there is one.)