We removed flanking almost immediately after 5ed release. It was too easy to get advantage... for the monsters. This was resulting in a lot of tpk at first. During one of our Friday night D&D a few spectators asked us why we had removed the flanking.
We showed them this scenario
A group is attacked by 4 ogres. One of the ogres start a grab with the fighter, succeed and immediately drop the fighter behind him. Very fast, the fighter is surrounded by four angry ogres which will attack with advantage. Now imagine this scenario with low level characters and 6 hobgoblins...
Yes when advantage is in favor of the players it is powerful. But in the hands of the monsters, it is deadly.