I personally like going through it all manually.
Found that some drop rates are insanely low and some are oddly high. either way you can create a fully custom drop list if you do it yourself, each cave you know the different drop rates, rather than a global 2x drop rate multiplier e.c.t.
Doesn't take long, same for mongen (done that myself too)
Taking the easier and quicker option for stuff like this isn't always the best idea, individual control is so good, you have an issue with 1 mob you can isolate it, drop rates are too high, you still got to change them all..
Effort is rewarded