Peroxide has its place, but it doesn't have as much effect on protein as it does on iron. I don't like to make the stains harder to see before I have had time to deal with them.
Blood is typically neutral pH (diet, etc. dependent of course), hydrogen peroxide is a weak acid. It will break down the proteins in the blood, helping to break up clots and loosen dried particles. I never compared the ability to clean out iron vs. blood, fact is that it works - no need to impose methods by stating that something won't.
Physical vs. chemical cleaning. Have something work for you instead of you working for it...
A combination of light scrubbing after/while soaking the area with H2O2 is a good bet!