The Constitution explicitly grants Congress the power to define the Supreme Court's appellate jurisdiction. See Art. III, sec. 2. The Framers never envisioned, obviously, that the Supreme Court would become the only unchecked institution of the federal government.
The SCOTUS is not unchecked. The Court's time-frame (many decades) is necessarily -- and by careful design -- much longer than those of the Executive and Congress (6 years or less). Justices are placed on the Court for life, but all eventually retire or die.
It is only our (understandable) impatience that causes us to not see the Founders' wisdom in having one of the three branches work in very long periods.