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.
On its own it is not that bad an idea for someone who carries a mandate of the majority of the population to be able to grant pardons.
Taken to the extreme, we could have an impartial legal system putting in prison criminals from an even mix of society, and then the president pardoning everyone from the majority group, leaving in prison only the minorities.
And how would you call a justice system, so complicated and convulted and therefore expensive that poor people (from minorities) don't really stand a chance to get their justice there?
Obviously Ross was not in that group, but I see presidential pardon as a potential tool to counter the flaws of the justice system.
And till those steps are implemented, don't you think you would enjoy it, if the next president would pardon Snowden, or your personal favorite case of unjustice?
This might be a good first step, too. Read more books from a time when people were struggling with arbitrary justice.