I saw the raw and got a glimpse of it and I can say, It had the potential but if you make the mc growth the same, the story will continue to be boring, its best if the author decided to make mc have a growth to make feel that he should start having a goal that make him more mental stronger, because typical mind weak mc is not nice if the mc doesn't choose to grow.
I agree with you. The story had good potential but the pacing is terrible. It's good to take it slow if it's for the sake of the story, the character development or the world building. But at the moment: it's just feels like it's just the story lagging (looking at the raws it looks like it will continue this way).
It's kind of painful to see how the MC still degrades himself while the weaker game MC is allowed to shine. As already mentioned, it doesn't make sense as their are also other isekaied characters (one of them already changed the story).
One to reason to read these "I was reincarnated/ isekaied as a mob character" mangas is to see the characters evolve and give them character growth. But the MC tries so hard to keep a low profile and to live a depressing life that it's just depressing.
One major flaw of this story is the relationship between the MC and his fiance which is stagnating. I know that many people hate her because of abandoning the MC at the beginning. I actually think that this was the intention of the original mob Butao. Looking at his relationship with his family and how he behaved at school it feels like he was self-sacrificing so that his love could live a happy life (maybe he thought he was no good because of his skill). In the talk with his family we learned that he entered the school to protect one person which is probably his fiance. The MC and Butao seem to share their feelings somehow, so he is not interested in other girls. Deep inside he only loves her. But still he's so focused on maintaining the original story that he's willing to get NTRed by the game MC thus ignoring the feeling of Butao.
The story between MC isn't progressing (in my opinion it was the driving force for original mob's actions) for an eternity. He has feelings for her bit doesn't act, she gets glimpses of his change but keeps sticking to the game MC, but we have the usual lack of communication (it really feels like rental girlfriend; one step forward, two steps backward). They just lead separate lives (which can best be seen when they walk to school). The few occasions when they talk don't progress their story but are just depressing at this space.
The MC's only goal is to maintain the original storyline and becoming strong enough to protect his family. Otherwise he is just like a spectator which has become quite annoying after so many chapters.
To sum it up, these kind of stories should originally cause a good feeling seeing an underdog succeed. The MC (sometimes, not all the time) self-sacrificing himself is also OK. But an MC not pursuing any happiness is frustrating.