Larian's handling of Advantage largely breaks the 5e system, it's rather fragile really. In short, they hand Advantage out like candy. For example, one can get Advantage by simply walking behind the target, that's Advantage at no resource cost. This invalidates a host of abilities and spell effects that have a resource cost, or are unique aspects of certain classes. Largely, the sole utility of these abilities and spell effects is to offer Advantage to yourself or your team-mates, usually with the target getting a saving throw in the process, now it's free at no resource cost. This is some newb-ass design by folks that don't know how the various spells and abilities of 5e interact. The unholy union of D&D 5e and DOS has a host of other problems as well, but this handling of 5e's key system is the worst.