Early game is very important in TFT. It’s much easier to make 1 cost units into 2 and 3 stars, and they have longer staying power because of the short game length and the strength of items.
Mid game units add 3 and 4 cost units to the pool. It is expected that they are level 1 or 2 when assessing this power level. Most of the units you acquire from this pool are going to form the cornerstone of your comp along with the strong early game units. Final setups will start to come online and if you are playing against players with tight builds, you will lose HP quickly if unprepared.
Late game adds the Legendary 5 cost units to the pool. Most of the time, these come online too late to make a difference, and seeing them 2 starred is rare, so we will keep that in mind.