...when the story pretty much wipes the comics out of continuity.

Spoiler:
The character of Maerlyn is easily the Big Bad of the DT universe in the comics, here he's friendly and akin to the actual Arthurian one. He's also enemies of the Crimson King and Walter, the latter of which he's unaware that he's his father(!). I guess you could say that the story is unreliable, though given that it's a "legend".

The idea of Marten knowing that Gabrielle will be shot by Roland also changes the concept from the comics, where Marten is planning on Roland shooting his father instead but his jealous sister/lover the Grapefruit (ugh) rigs it so that Roland shoots Gabrielle instead.

Plus as has been stated elsewhere in the comics Roland is imprisoned after his mother's death and Steven dies soon after so there's little room for Roland to be sent on his quest.