Konjiki No Moji Tsukai - Yuusha Yonin Ni Makikomareta Unique Cheat - Chapter 27 The Awakening Of A Trick Art, Part 1

Two things I don’t get:
First how do LVLs work?
Arnold dude is lv 37 but seemed to have live a quite long live, guessing he in his 30s?
He seemed to be strong and experienced enough to know how to lvl up.
I get that mc is probably OP cuz other worlder, but how the f does that oppai loli work?
She 14 already lvl77? Lets assume that gaining exp is equal for everybody, so how did she lvl up so fast? with no party at that?

And the other thing I don’t get is the intelligence of MC:
He has an OP like magic, but the only down side seems to be his intelligence.
For example he doesn’t know how long flight will last: Test it out!!! No one tells you to fly over 30cm above the sky. When you fall, you wont get hurt and know how long it lasts.
At lot of guessing and trying out at inconvenient times for someone reads a lot and should know better.
Also doesn’t use his peek on other peoples status, when this is probably the most Op ability he has, and then he wonders why other people turn out to be a lot stronger than he guessed.

But then again thats the difference between knowledgeable and smart.
I guess he knows quite a lot cuz of books but is actually also quite dumb. Like Oppai loli-lvl dumb.