The Minoans provide them a range boost of 2 to Composite Bowmen, allowing them to strike before other archers and out-range towers. The Minoans can also continue to use them effectively in the Iron Age.
The Composite Bowman is better than the Improved Bowman. Civilizations that can train the Improved Bowman usually have the ability to upgrade them to a Composite Bowman. Because of this, the Improved Bowman never really makes their full appearance in a random game. Boasting solid overall stats, the Composite Bowman is an excellent ranged choice due to its low cost.