Not having a pardon power allows bad judges to throw anyone they don't like into jail with no recourse by anyone.Technically, all judges can be impeached, and all judges other than SCOTUS can be appealed (there's actually a specific writ you can file claiming to be jailed unjustly, habeas corpus).
In practice, impeachment hasn't proven to be much of a check on judicial power (recall elections have probably been more effective overall), but I think the appeals process more or less works and I don't think the pardon power has added much, on balance. I think unilateral pardon power by a political official has proven sufficiently ripe for abuse that I would even support adding limits like some kind of Congressional check, but it's definitely nowhere near a top priority.
Obviously the appeals process has had plenty of failings too, the Japanese internment camps being the most famous example, another high-profile one is Lincoln suspending habeas corpus during the Civil War.