Multiple sources of Advantage do not provide anything, only when trying to negate Disadvantage along with gaining Advantage is the only time it's useful.

Also, totally agree and keep forgetting to mention, being in Low Ground also should not be providing Disadvantage. Not only do High Ground gain Advantage, but also Low Ground gain Disadvantage is such a HUGE swing in roll percentages.

This is why individuals, including myself, have suggested Larian implement a Cover mechanic and then High Ground just provide a small +To-Hit bonus.