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.
Yes, every president has pardons that are arguable (Biden pardoning his son, for example). And anyone pardoned has been found guilty of a crime, by definition. But not all crimes are equal.
Pardoning 1500 people that participated in a (luckily failed) insurrection that caused 5 deaths and 100+ injured, is an extremely bad precedent, and sends a very bad signal.
Pardoning people convicted of marijuana possession (like Biden did) is not the same thing as pardoning the head of the worlds biggest guns and drugs marketplace. Even if he did not kill anyone himself (it was proven, just to a lesser extent, but fine). Those drugs and guns most definitely did kill people.