There are a few issues here:
First, hide drops are NOT affected by 'drop chance' percentage. Never have been.
Second, the issue of hide drops decreasing as the level-difference increases has been discussed many many times and will not be modified. If you cannot get the hides you need, then you must fight higher level opponents, or buy the hides. You should have noticed this throughout your character development, since you are now T5.
Third, the drop chance for other items is also affected by level-difference, and has been for a loooong time. This is nothing new and you should have seen this, and adapted to it, by now.
I don't mean to sound harsh, but by Tier5, you should have noticed this stuff by now and seen it mentioned in the forum many times.