The author should've started with this, it's actualy way more intresting than before the flash back.
I kinda agree but also don't.
I read the wn/ln, and the "In Medias Res" storytelling really works. Because you often have characters from her past show up and move plot forward. It adds a fun little dash of mystery to the SoL, where you learn bit by bit more about her and her past, and her capabilities. It's pretty natural, just like you learn about people in real life.
That said, it's a real waste to just speedrun the origins in a flashback towards the ending of the manga. So dumb to just tell a interesting flashback and then end it. And the story in general probably could've used the manwha/manhua format, which opens the series with a flash forward of some kind, where the series reaches eventually(in this case, it would be a flashback)
All that said, a story that starts with this, goes through her adventures, would certainly be more engaging. Even though I think the Slice of Life works well with in Medias res format, it can get dry at times in this story.
Perhaps a "Arrow"/Tengoku Daimakyou style format would be most optimal for this story. Where the main narrative starts in present time(receptionist) but there is a secondary plot where the past story progresses. With both building/relating to the other story, until things reach a climax and the story unifies in just the present going forward.
Or even something similar to Kumo desuka which told the story in split for at as well(Spider from the beginning, alongside classmates in the academy(future).