Let me play you a sad song on the world's smallest violin:
1) Kerrigan ripped off a steel door in Queen of Blades, so there's no way any comparisons to her & humans can be made.
2) Kerrigan's arms aren't as dangerous as her wings.
3) There's alot more to strength than muscle mass - such as the amount of motor units that can be recruited.
4) Kerrigan & Zeratul increase their strength with psionics, and they're both way more powerful than any humans.
Yes, Zero could shoot a Zealot and kill it by sneaking up on it via cloak or something. But in a direct 1v1 it would lose, for reasons I already mentioned:
As I've been saying for the last page, the
Protoss were still there after that mission. And they were on the ground fighting. It's in the post-mission text for the New Gettysburg mission.