Kat definitely isn't safer than Kha'zix. She has to sit in the middle of the enemy team to use her only ability that scales well, and it's channeling. Shunpo requires a target, Kha'zix E does not. Kha'zix's ult pushes his survivability over that of Kat's.
I won't compare him to Leblanc, because Leblanc is Leblanc. It's also unfair to compare a jungler to a midlaner, as midlaners typically have a lot more farm (unless you're Yi or something). However, Kha'zix doesn't use his CDs then flop around uselessly while he waits for them. His Q is very spammable, and his autos hit very hard. He can also build a couple of defensive items and still do excellent damage.
Kha'zix is gated by isolation because his Qs hit for over 1000 damage late game on a 3 second (or less) cd. Kat could use all of her basic abilities and barely reach that level of damage.