@Qelix Yes, at least by what I understood from Google Translate. I haven't read the LN, but I really hope the MC being stupid it just on the Manga.
@KuroAnsatsu The Goddess talked about it on the first chapter, that all reincarnators (except the MC) didn't figure out the trick to become stronger using the Skill Board. A lot of people talked about it on comments, they probably thought that it was like a game and picked skills based on some build.
Considering how short the current chapters are, the whole explanation about why the MC is strong but he's still called "Inferior" will probably happen around chapter 10 or 20.
I can write about it using the spoilers if you guys want.
@icarushector I just put the link here then:
http://ncode.syosetu.com/n8516fu/