Part of Australia's side less than three years ago, Warner was the most vehement critic of his old teammates on Saturday as they spiralled to a 176-run loss.
The former opener has often been outspoken in his criticism of selections in recent months, but took his criticism to a new level on Saturday as Australia fell to 8-62 en route to a 176-run defeat.
"I'm just upset, it's terrible, it's un-Australian. There's no fight whatsoever, it's disgraceful," Warner said on Fox Cricket.
"Chasing 288, you're winning a Test match, you could win a series, it's on the line, and this is the way that they're playing.
"I think it's deplorable but the batters have let the bowlers down the whole series.
"Matt Renshaw showed fight in that first Test, but I think the batters have been utterly disgraceful."
Australia's batting issues have long pre-dated this tour, with the side 4-95 in worse in 14 of their past 25 Test innings.
Asked what he made of Warner's comments after the loss and if they were fair, Cummins responded: "I don't even know what to make of that".
Warner was not alone in his criticism of Saturday's collapse.
Mark Waugh labelled it "terrible" on the same Fox panel, while 56-Test veteran Simon Katich also hit out in SEN's radio commentary.
"This has been brewing for a while," Katich said.
"And the rhetoric is the batting group has had to deal with bad wickets. Well the wickets in this series have been nothing bad about them."
Katich also pointed to Australia's two-day defeat at the MCG last year, their day-one batting in the shock loss to Bangladesh in Darwin in August and last week's 99 in Gqeberha.
"If you constantly keep making excuses for players they will latch onto them," he said.
"This is exactly what Matty Hayden was talking prior to before the series, about mediocrity.
"If you're going to allow that mediocrity to grow, this is the sort of performance you get."
Katich has been a long-time critic of the suggestion players should go after the bowling on tough wickets, with the theory they will be dismissed eventually.
Much of Australia's best batting in South Africa has been in patient innings on flatter pitches, as evidenced by Renshaw's Durban century and day two in Cape Town.
But they were seemingly drawn into the chaos on the fifth morning of the deciding Test, with Travis Head out driving outside off at 2-22 and Alex Carey reverse-sweeping at 4-42.
"I don't think we've be able to manage those different tempos well enough. It's something we talk about," Cummins said.
"This series, a lot of the runs that were scored were on the back of those old Test cricket kind of values that you face a lot of balls, it gets a little bit easier.
"It's not always the case. So, I don't think there's one set rule.
"But, certainly here, even in Darwin, there's moments where you will get rewarded. The game will come to you if you dig in.
"That new ball was going to be a key period ... But if you can just get through that period it does get a little bit easier against the quicks."
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