If the downspout makes one end of the bed too wet, consider a project for one-of-these-years.
Add a right-angle bend to the end of the downspout, and run another "downspout" horizontally the length of the bed. Give it only a very shallow drop, like 1-2" per 10 feet.
Maybe make it from short sections you can separate later if you need to clean it out.
Drill small holes along the side, near the current end of the downspout.
Drill larger holes on the bottom, at the far end of the bed
Drill intermediate-size holes near the bottom of the side, in the middle of the run.
Hope that water comes out more uniformly and waters the whole bed evenly.
Alternatively, where the bed is water-logged, make it a raised bed and cut a slit trench along the side of the bed, draining down to some lower spot. Run the downspout into the slit trench and hope most water runs away instead of drowning roots.
