I define Teshuvah 3 ways
Those who've sinned need to Repent
Those who've been challenged by life or by G-d need to Respond
All Jews, Sinners and perfect Saints alike need to Return to G-d. Thus a Tzaddik Gamur does Teshuvah by Returning [even closer] to Hashem
A Teshuva Sh'leimah, undoes all the damage retro-actively. It is as if no evil has been committed at all. Technically speaking, there is no sin left to punish, no damage to rectify anymore
I see Kapparah [CPR] differently. Here too I offer 3 definitions
2. Redemptive Payment
3. Covering or Insulating
[EG Kapores or v'chafarta osah mibayis ...]
Atonement to my way of thinking is LESS desirable than a complete Teshuvah
Teshuvah is like a cure. Kapparah is like a palliative.
EG a person's cholesterol level goes up.
The cure would be a diet and exercise regimen that would both lower the cholesterol and remove any plaque buildup
The "insulating" method would be like taking statin drugs to protect one from any ill effects of the high cholesterol, but would not be a cure of the underlying syndrome, just a treatment.
Ideally we shoot for complete Teshuvah. Kapparah is nice in case when we fall short of our loftiest ideals.