I wish I had done my research before finishing the quest. I can confirm that if you pick warrior's side you will not receive Meridia's 5th light. I don't think that the quest presented enough hints to the fact that you are making the "wrong" choice by picking warriors as supposed to scholars (for instance, in Sheogorath's quest you are told that by saving Valaste you are giving up on "half a dozen of skyshards"). The sad part is that I cannot go back and "fix" my "mistake". I obviously won't reroll my character at this point, but I do think that they should implement a retrospective achievement granting.
Player choice should not have THIS much impact on the game. I can live with that fact that the game didn't give me a certain weapon, a certain amount of gold and even some extra skill points, but I cannot be happy with the fact that I won't be able to achieve full completion.