Police have accused the Manchester Arena operator of failing to devote the "time and attention required" to security before the bombing that killed 22 people.
Greater Manchester Police (GMP) accused SMG, a US-owned firm, of seeking to shift the blame to "mask its own inadequacies or deficiencies".
The arena had "failed to keep the masses safe" and relied on free advice from police when it should have employed an expert, GMP said.
Police also blamed Showsec, the security provider at the arena, saying that the measures taken were "sufficient to have either deterred or mitigated this attack, if only they had been implemented".
The comments were made in closing statements on arena security ahead of a report expected from the inquiry chairman in May.
Salman Abedi killed 22 men, women and children when he blew himself up in a suicide bomb attack in a foyer outside the arena at the end of an Ariana Grande concert in May 2017.
Ken Upham, a GMP counter-terrorism security adviser, has been criticised for giving "over optimistic" scores on security assessments at the arena.
SMG, now called ASM Global, said he gave them a "false sense of confidence" in their protective security measures and should have advised them to push out their "security perimeter".
Andrew O'Connor QC, for SMG, described Mr Upham as a "highly trained expert" who at "no point" had offered "any note of caution about his ability to give broad advice, or about SMG relying on it".
There has been "no evidence" of Mr Upham proposing changes to the security operation in the arena's City Room that were rejected or ignored by SMG, Mr O'Connor said.
SMG also said Showsec should have sent stewards to confront the bomber and they would then have locked the venue down.
But Richard Horwell QC, for GMP, said: "Blame or criticism is common place in a public inquiry. Sometimes it is justified but it can also be directed by a core participant at other organisations or individuals in order to mask its own inadequacies or deficiencies."
Mr Horwell added: "We do not accept that the evidence supports those contentions and we suggest that SMG simply did not devote the time and attention required to ensure that its protective security measures were properly and effectively applied."
Mr Upham offered a "free and limited service" which was "purely advisory" and did not have the time to spend "days or weeks at this or any other site", the lawyer said.
"He was required to make just two formal visits each year, each visit lasted about two hours only and we contend that the limited amount of time he had would have been obvious to SMG."
Regarding Showsec, Mr Horwell said that "security was only as good as the proficiency with which it was delivered and the degree to which plans and procedures were followed".
He added: "The security measures were in fact adequate and were sufficient to have either deterred or mitigated this attack, if only they had been implemented."
Mr Horwell said: "Our point is simply this. Mr Upham made mistakes; he was not perfect. But the spectacle of SMG blaming him for its deficiencies and inadequacies has been as unattractive as it has been unfair.
"The responsibility for the safety of visitors was that of SMG alone. The problem was not the advice, (it) was the implementation of that advice."
Lawyers for Showsec said the company could not be held responsible for the safety of the parents who were waiting for their children outside the arena doors, and who made up half of the 22 victims.
Jonathan Laidlaw QC, for Showsec, said it was "not by any means clear" that the company "owed any protection-type duty to members of the public who were not attending an event, whether they were in the City Room to meet those who had attended an event or whether they were passing through".
Instead, he said the "primary responsibility" for the safety of the public in the City Room - a thoroughfare which also included the arena box office - rested with the police.
"Primacy for combating the risks of a terrorist attack lies with the state and is exercised through its security and police services," he added.
The inquiry continues.