I just can't agree with this, the manga is extremely clear that they're not being optimistic, they're just completely broken.
I highly disagree with that interpretation based on the manga and authors comments.
Broken? No. Tired? Maybe yes. In the end they are still pushing forward, looking for work and maintaining the small moments for themselves. They say this. They think it. The manga shows it. The manga ends with it and then the extra (especially, including the last pen sketch) doubles down on it again. Just because they didn't get everything they wanted doesn't mean life is over and they're done. They're "strong girlfriends" as they say and they intend to try again with new valuable life experience. It just doesn't end once they've found a job because it's making a point about the unknowable future and their drive.
It's just a "real" story. If I met two people like them (and if we're all old enough we likely have) "broken" is not something I'd ever use to describe them, especially not those two. Whether their story is viewed pessimistically; and whether one views any real person in their position pessimisticly, is again up to the individual. But the characters do not view themselves as broken and aimless. They're not wallowing in misery. They're still on the road, just like the final chapter ended with.