Well, if you thought of those small flashbacks its not really that hard to think about? they got suddenly transported, got a system, confuse and didn't know what to do, it was Mc who step up first about no matter what they need money to live first, parties are formed and separated, live their own lives and adventures, and time skip after that. 3 years in the other world is long enough to learn various knowledge of that world. And a clue of Mc's Earth life, if you see Mr. Kim's stuffs he brought out, there was a mag with Dr. Kang's face on it. I guess Dr. Kang is a famous doctor on earth that's why he call MC as Doc.
I feel like we shouldn’t have to guess
We are starting basically from the middle, though I have to disagree with your points. I feel like that you are not the audience for the story: this story is most enjoyable for a reader who enjoys guessing what has happened. This is like a detective story in manga form.(￣∇￣")
Yeah this type of storyline definitely isn’t for me, I like a build up.
It feels like I haven’t started from the beginning but middle of the story barely any explanation for why he’s strong or has all this knowledge. So kind of confusing.