It's an essential part of the system of checks and balances among the three branches of US government - it prevents the judicial branch from getting too much power compared to the executive branch.

People who are guilty of a crime and prosecuted fairly under the law should generally serve their sentence. Exceptions to that are best managed by an independent and transparent tribunal who can give principled reasons for commuting specific sentences, for example a prisoner serving a very long term has undergone a genuine moral transformation and is now safe to release, or changes in society have rendered prosecutions of a certain time and place anachronistic and unjust be modern standards.

Yes, such a system could be (and has been) abused, but given the power the judicial side has (and how that power can be abused) there has to be a system in place that checks the judicial system's power over individuals. This check prevents over-corruption in the judicial system to an extent.

The point is to not allow any branch of government to gain too much power - a "separation of powers".

Given some presidents have pardoned HUNDREDS of people this would imply there is a serious problem with the US justice system?

Thankfully a US president can exert his king-like authority and correct this judicial problem.

Question - Given the obvious flaws with the justice system how does one get the presidents attention to get a pardon?

Have you ever looked at the people who were pardoned and the crimes they committed?

Armed bank robbery, drugs, fraud, counterfeiting.