Is bringing Sara Lance back via the Lazarus Pit a good decision? Probably not. But fans love her, and she has to come back somehow.
She would either have to come back at the hands of an enemy or a loved one, and the decision was made that her sister would do it out of love, despite the pitfalls that might come as a result.
Not only does Sara need to make her way to DC's Legends of Tomorrow, but John Constantine has to make an appearance. That means that what goes down in Arrow Season 4 Episode 3 is unlikely to go well. Oliver will probably have to use those mystics he's run into before to clean up a mess Laurel makes reviving Sara.
Let's not hold it against her, OK? You wanted Sara back, and she's on her way. She's coming by way of love. And, she'll be fixed by another great character gone too soon, Constantine. All is hardly lost, just a little wonky. And temporary.