Going by the end of the chapter, the princess power and grandpa inventions are because they're probably descendents from other people who was isekai'ed in the past.
I've been wondering on why Takeshi simply woke up in the other world after dying, while his classmates were summoned.
Hypothesis, the goddess from time to time summon people, either to try change / advance the world, or for her own sick amusement, I wouldn't be surprised if the Demon King was one too and she summoned the entire class to kill him because things got out of control.
Now, this is probably just me expecting too much of the mangaka, but what if Takeshi suffering is all the goddess doing? We already know he's level 0 and has a mysterious skill, so what if he's a counterbalance to his classmates? She purposely made that naturally bad people all ended in the same class, then she made their leader push everyone into being even crazier and bully Takeshi, just to ensure he would want to kill all of them?
His mysterious skill might even be a debuff to his classmates, make them irrationally hate him, ensuring they'll screw up one way or another during their confrontations, he might even had it while on earth.
Literally plot armor as a power.
TLDR
I'm probably putting more thought in the story than the mangaka is