This can only be considered a "flaw" if one assumes 1) the arbitrary requirement that a macguffin must affect both the outcome and protagonists of the film it first appears in (assuming a series), 2) that the search for Luke was intended to serve exactly the same purpose as e.g. the Death Star plans, and 3) the sequel films must conform to the same story structure as the OT.

First, analogizing story structure to the OT is flawed. ANH had to be a standalone film, because there was no guarantee that sequels would ever be made. ROTJ was intended to end the story (simply put; there was waffling from Lucas about weather he'd eventually make sequels, but that's irrelevant), which necessitated every plot thread be wrapped up. I'd argue those two things factored into the self-contained structure of those films far more than some deliberate attempt to ensure that "the primary goal must affect the outcome of the story." That leaves only ESB, which unsurprisingly is the weakest fit for your point, and happens to be the closest contextual match for TFA (continuing a story and leading into another film which will certainly be made).

While the search for Luke taps into many of the same purposes as a standard "driving force" like the Death Star plans -- setting the story in motion, intertwining the stories of the characters, driving key decisions, etc. -- it also has some crucial differences. TFA faced a challenge the OT films never did; it had to introduce new primary protagonists while continuing the stories of the old ones. I think this fact largely informs the odd story structure with regard to Luke. The search for Luke accomplishes the aforementioned plot tasks in a way that leaves enough space for the new characters to be the focus. That fact illuminates the true purpose of the Luke story: it's a trick.

The search for Luke has no real impact on the story of TFA because it's merely a means to incorporate the OT characters in a profound, ever-present way while allowing the new characters to be the true focus of the story. I say ever-present because from the opening crawl line to the ending, Luke is always hanging over the story. That was almost certainly done deliberately to make the audience feel they are watching a Star Wars film, a continuation of the previous story. Yet the audience only thinks they're watching a story about finding Luke, while what they're really watching is Rey's awakening. The force itself is really what Rey is pursuing through TFA, not Luke. She builds her connection to it until finally using it to defeat Kylo at the climax of the film. Luke is just the lead-in to the next film, and the connection for the audience back to the OT.

tl;dr The search for Luke is a variation on the more conventional "primary goals" of the OT, necessitated by TFA having to incorporate the OT characters while making the new protagonists the true focus of the film. It somewhat defies convention, but it's hardly a "flaw" as long as TFA told a satisfying story, which consensus seems to indicate it did.