No, It Is Actually An Idiom.
Yes, "merciless sky" is a metaphor that refers to the sky's unyielding or strict nature. It implies a sense of cruelty or harshness in the way the sky appears or behaves.
metaphor sky
a sky metaphoe is boobies getting attacked by monsters
The gray sky enveloped his mood like a shroud.
Merciless - Merciless album - was created in 2003.
like a ghost.
Blue as the sky
It is a metaphor because similes use the words "like" & "as".
Simile
it is a metaphor
Yes
You are the leader (in control) of your life.
It is a metaphor to dream big and that any average joe is capable of great things.