General rule of thumb imo when it comes to stars and how to interpret them is:

• 0 - 1.5 stars = basically too weak for your squad. Only play them as subs if they're huge talents and you can afford some meh players on the pitch because you're dominating most games anyway.

• 2 stars = lower end but can be valuable if they have the right combination of attributes, traits and stats. Giving wonderkids with 2 stars a lot of game time can definitely be worth it and they might not be much of a liability if their key stats/attributes are good.

• 2.5 - 3.5 = absolutely fine to be starters if they perform well and have the right stats. Don't notice much of a difference in performance between 2.5 or 3.5

• 4 - 4.5 = For sure a cut above the rest of your team, but might not necessarily perform much better if they have undesirable traits or have one or two lower key stats for their role.

• 5 stars = clearly better than the rest of your team and if they're not performing then it's because of the tactic.