It is a trend of essentially implementing game system into novels ... The MCs usually possess them and draw unfair and unproportional advantages from these systems to make them superior to their peers. The system (just a wish fulfilment vehicle) rewards them more or less for merely breathing in their average existence.
But to be honest, I do not think they are inherently a bad idea. As long as everyone operated under the same rules, they would be quite fair. But the systems favour the MC to an uncanny degree.