Their comments came as the Hague tribunal began hearing an appeal against his conviction for the war crime.
Krstic, 55, was found guilty of genocide in 2001 by the war crimes court for Europe's worst atrocity since World War Two.
Up to 8000 Muslim men and boys were murdered after Serb forces overran the UN-declared "safe area" in eastern Bosnia.
The Krstic judgment was a landmark because it established for the first time at the United Nations court that genocide was committed in Bosnia during the 1992-5 war.
Both sides are appealing; Krstic's lawyers say he did not commit genocide and prosecutors say his sentence is too soft.
"This sentence is manifestly inadequate in the light of the very extreme gravity of the crimes committed by the respondent," prosecutor Mathias Marcussen told the International Criminal Tribunal for former Yugoslavia.
Trial judges were wrong to decide Krstic bore less guilt than other high Bosnian Serb officials, prosecutors argued.
Most wanted men
Krstic reported to military commander Ratko Mladic, who along with Bosnian Serb wartime leader Radovan Karadzic is charged by UN prosecutors for genocide in Srebrenica. Mladic and Karadzic are the tribunal's most wanted men.
Krstic's counsel argue that he was wrongly found guilty of genocide, which the UN defines as the intent to destroy in whole or in part a national, ethnic, religious or racial group.
His lawyers claim he lacked that intent.
"This sentence is manifestly inadequate in the light of the very extreme gravity of the crimes committed by the respondent"
Mathias Marcussen, prosecutor
The defence has requested a re-trial, saying that ways in which prosecutors disclosed some evidence violated Krstic's right to a fair trial.
It also says judges erred on legal and factual issues, and did not take sufficient account of sentencing practices in Bosnia or of Krstic's personal circumstances.
Genocide is also on the charge sheet against former Serbian and Yugoslav President Slobodan Milosevic, who has been on trial in The Hague since February 2002 for war crimes in Bosnia, Croatia and Kosovo during the Balkans bloodshed of the 1990s.
Krstic, who pleaded not guilty after being seized by NATO troops in December 1998, was one of the most senior military figures to appear before the tribunal.
At the time it was issued, Krstic's sentence was the harshest the tribunal had handed down.