The Black Cats have won just one of the 10 Barclays Premier League games they have contested since the England striker headed for Aston Villa in a ?24million transfer, and taken a solitary point from the last nine to slip to within five points of the relegation zone.
They have scored only nine goals in the process and just two of them have come from big-money summer signing Asamoah Gyan.
Firepower: Bent has proved an instant hit at Villa following his big-money move
However, while many commentators have pointed to Bent's untimely departure and Sunderland's decision not to replace him, even with a stop-gap signing, at the pivotal moment, Bruce insists their problems have been at the back rather than up front.
He said: 'For me, when we were successful, the reason was our back lot. Our back lot was rock solid, we didn't give much away. Certainly when [Michael] Turner and [Titus] Bramble were in tandem, we kept four or five clean sheets at that particular time, and that hasn't happened since.
'For me, rather than up the front end, the one area where you need to be rock solid and create partnerships is at the back. You need that spine of your team and unfortunately, it hasn't really happened.
Off target: Record-signing Gyan (left) has scored just twice since Bent left
'But it is what it is. I can stand here and try to make excuses, but it is what it is.
'It isn't going to get any better - it certainly doesn't look as if it is going to get any better for this season - so we have to live with it, get over the over the line and address everything and analyse everything and understand the reasons why better than we are doing at the moment.'
Bruce's argument has some merit - his side have conceded 24 goals in its last 10 games with a creditable 0-0 draw at Arsenal on March 5 their only clean sheet.
Both Bramble and Turner have missed large parts of the season with knee injuries - indeed, the former may not play again before the end of the campaign with a cartilage problem - while loan signing John Mensah's fragility has become a constant and costly theme.
Feeling the heat: Steve Bruce is coming under increasing pressure from fans following the poor run
However, they have also been hit hard in attack with Fraizer Campbell having managed only four appearances this season and facing the possibility of sitting out much of the next, while Danny Welbeck, having just returned from a knee injury, damaged a hamstring in Saturday's 2-0 defeat at Birmingham.
Bruce has found himself in the difficult position of trying not to make his lengthy casualty list an excuse, but at the same time having to piece together a team from walking wounded and youngsters who in an ideal world, would be introduced more gradually.
He said: 'I can only try to give reasons for why we are where we are at the moment. For instance, one statistic is Turner and Bramble have played together eight times and we have lost once.
'Now we know even Chelsea with [Frank] Lampard missing are not quite the same; Manchester United when they are without [Nemanja] Vidic and [Rio] Ferdinand, not quite the same.
'Unfortunately, we have not been able to cope with the loss of so many for so long. It's caught up with us. We haven't been able to cope with having six or seven missing week in and week out.'
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Explore more:People: Darren Bent, Steve Bruce, Danny Welbeck Places: Birmingham, United Kingdom