"Relentless" and "unyielding": understanding their distinctions

What is similar?
Both "relentless" and "unyielding" describe a quality of persistence and determination, indicating refusal to give up or relent in the face of obstacles.
What is different?
"Relentless" often implies continuous and intense action without pause, sometimes carrying a negative connotation of being harsh or oppressive. "Unyielding" emphasizes firmness and resistance to pressure or influence, highlighting steadfastness and inflexibility, often in a positive or neutral sense.
Which one is more common?

Examples of usage
Relentless- She was relentless in her pursuit of excellence.
- The relentless rain showed no signs of stopping.
- Their team faced relentless opposition throughout the match.
- He maintained an unyielding commitment to his principles.
- The unyielding material did not bend under pressure.
- Her unyielding spirit inspired those around her.