Regular Archers and Slingers get 7 and 4 respectively for Missile attack.
Cretan Archers and Rhodian Slingers (both of which seem to always start off with 1 experience) get 12 and 10 respectively.

Elite units rack up kills more easily and therefore appear to advance in ranks faster. After 7 turns and 7 battles, that 1XP Cretan Archer unit has made 476 kills and is now a 5XP unit with 16 Missile attack. By comparison, a regular Archer unit in Syracuse which also participated in some heavy fighting Vs Scipii and the Carthaginians has now gained 2XP from 156 kills from 5 battles in 7 turns.
I will agree that Archers don't do too well against well armored foes. It takes many volleys to cut down a General's Bodyguard unit. Cretan Archers usually average around 1-2 kills per volley against them. But in the early game, there really aren't that many well armored units and getting both Cretan Archers and Rhodian Slingers for the Greek campaign means that armies having them will be able to execute early rushes easily Vs masses of Militia Hoplites, Light Lancers and Peltasts.

Also take into account the fact that the AI likes to plug Wooden Wall/Palisade breaches with units and rush around while getting shot for fun and also that town square AI again allows free murder while standing still and getting shot from the back. So all in all it really would be nice to have some adjustments somewhere, be it AI or just simply reducing stats.

It's true that friendly fire is more of a problem in R:TW but I tend to put archers a little in front of infantry or beside them anyway so I haven't found this too irritating. A quick charge by fast enemy cavalry has the risk of decimating the archers but if you time it right, your archers should retreat in time for your infantry to charge forward and engage the enemy cavalry.

Anyway perhaps I should stop playing and wait for the patch. The devs appear to listen to the fans so who knows they might overhaul the AI quite a bit...