The readiness system did play a role in the game, but not in the way that it should. When gathering forces on the Citadel, one would expect those forces to be shown fighting the Reapers in some way. When one took the time to gather support from various alien factions, one would expect it to be shown to have made a difference, perhaps in the winning of the war, or at least the weakening of the Reaper forces.To counter some of your points:
- The readiness system wasn't pointless. In fact, it was the whole "point" of the game. It helped to make things truly stand out as an intergalactic war, leading you to find allies all over the galaxy.
Unfortunately, the EMS number was used to determine cutscene choices, with results that had little to nothing to do with what an effective military strength would effect. For instance, if one had a low EMS,
the destruction of the Reapers would result in Earth being scorched
save Earth from being burned
I wouldn't say that the EMS was pointless, but rather that the disconnect between expectations and results in that number made the effort seem wasted.