Stars only give an indication of how the quality of a player is compatible with the complexity of the level you are. So,for your level those players will be legend,for a +5 higher level they will be normal. Nothing strange.

Before a match,you have to compare the quality of your main team (the players you consider most performant),with the main team of your opponent.
Many managers may choose to have a 6 star main team,and a group of reserves with 1 or 2 stars.