What does he ask Hashem to do?
Rashi: He should cut off the corrupt judges from Yisrael.
Radak: Since the judges do not judge Emes, You must judge the land and do Mishpat for the poor against their oppressors.
Malbim: He asks why Hashem speaks to the corrupt judges, that they should judge the land, and they will have a share in the land like Elokim. They will not inherit the land, for they are destined to die! They will not judge it properly. You should rise and judge, for You created it and possess all Goyim, for it is Yours forever. You should establish it via Mishpat!
Why did he say "Atah Sinchal b'Chol ha'Goyim"?
Rashi: You possess the Goyim; all is in Your hands to judge it.
Radak: You possess the poor and their oppressors, from whatever nation they are. They are Your inheritance, for most Aniyim and oppressed people are of lowly spirit and truthful.
Malbim: Refer to 82:8:1:3.