Flair Blinds

Krillin could easily sliced into two pieces with Freeza disk Destructo after blinded with flair Sollars.

Well, thats because Krillin is a fool weak and it sucks. But not really, I think it was really just for the progress of history have been developed Goku would go super Saiyjin.

I have no idea
Perhaps the disc out so that he could not concentrate

but again:

Why did Goku / Vegeta does not kill the cell where he had the chance
Gohan eventually end cell

Krillin has unfortunately not been the main character this time

and gohan was supposed to be the main character instead of his father, but the author has decided otherwise at the end, so Gohan has become what his mother wanted him to become Alway (nerd, sorry me, this is not bad, at least he has a job)