I suspect that the idea originally was to give some safety valve but if it is used more than a few times by a President, it makes a mockery of it and it should be removed as a power. How can a President ever decide that the entire legal process is flawed and their opinion is right? If the sentence was too long then change the sentencing guidelines.
1500 in jail for protesting in DC? Really, less than that in jail after months BLM riots afaik. Sure, jail a few bad boys, but 1500? No way.
Throw a rock at people in power and go jail. Rape and murder is fine, no threat to DC.