Seven Deadly Sins is closer to Dragon Ball franchise than it is to Fairy Tail. Not only is the artstyle sort of similar but also because of how they handle fights, the introduction of "power level" in Seven Deadly Sins is also a supporting evidence for that.
Fairy Tail on the other hand, started as a One Piece rip off that didn't quite understand how to actually do the whole friendship thing and used it as a plot crutch 24/7 until it drove the shit down.
And Seven Deadly SIns easily has far better writing than Fairy Tail, but only really because Fairy Tail's writing became utter gutter after the first few actually good story arcs. But at least Seven Deadly Sins has a vision on what it's trying to do and where the story is going, and does it quite alright.