There is hardly any hard data on this... but even more rumors

Most of it is only based on experience and personal observations/theories
which can vary a LOT from person to person and their individual situation.
If we consider the rather small number of chances e.g. a drop x with high ee will appear
and anything that might happen eventually there is just too much room for "general luck" to make its effect...
Someone may play with godly gear for years without finding something, others may be lucky with 2 great finds on the same day.
As a result, it makes it even harder to observe something more reliable
and its extremely hard to make any general assumptions on the exact effect or degree of this effect ml has.
Personally, i tend to suggest to take ml as a welcome benefit - if you can afford it.
It doesnt hurt and was made to have a certain role in the game.
But:
All the ml in the world wont help if you are unable to kill mobs and do it in a good speed to kill more after.
This is the key to success sooner or later in my view: Endurance to play in general and the killing speed/success rate.