Ross said the pair were trying very hard in training and on game days but "it wasn't happening for them".
Trego - after returning home injured last summer following playing one game - scored a century in a Shield match this season but nothing of substance in what he was primarily hired for, T20.
In beating the Stags by 25 runs at Saxton Oval, Nelson, a day after Boxing Day, Northern Districts Knights coach James Pamment had described Trego's batting effort as "swinging like a rusty gate".
Cobb, who arrived just before Christmas and went sightseeing in Queenstown with Trego, has impressive credentials but also had nothing to write home about.
Mentally or otherwise the players' resumes didn't stack up in the New Zealand domestic arena.
Ross hastened to add CD's woes weren't just about the misfiring imports but also the core of "locals" not turning up at the park.
"It's not all their [imports'] fault."
The inconsistent top-order batsmen have failed, although some selections have to be questioned when players such as William Young and Ben Wheeler found themselves running out snake lollies while CD persisted with imports and batsmen "struggling at the top".
"The core of the squad, rather than the pros, should be the cream, leading from the front," Ross said.
"You can't have them propping up the team."
He felt there was no quick fix as the Stags needed to keep working on their batting and bowling skills.
"It's a double whammy when our own players are inconsistent."
Teams such as the Wellington Firebirds and Volts had core home-grown talent doing the job.
Andy Ellis and Dean Brownlie were also proof of that for Canterbury.
In previous seasons CD had the experience of the likes of Michael Mason, Ewen Thompson and Peter Ingram.
"With Skippy [Mathew Sinclair] retiring [before this summer] we knew he was scoring most of the runs last year," Ross reflected but said they couldn't blame that on their lack of success. CD had to face up to life without Sinclair.
It was imperative, he said, to understand Sinclair made the decision to retire for the future of his family.
"We never tried to hold him for our tournaments."
Spinners Marty Kain and Tarun Nethula were in sync as was cricketer-for-hire and ex-Black Cap Jacob Oram.
Next season CD will look at, among other options, recruiting imports from Australia.
ND, through the connections of their Australian CEO Peter Roach, have secured the services of fringe Big Bash players for their T20 campaign.
Ironically former Essex allrounder Graham Napier, who prematurely left injured from CD two seasons ago, is in fine form for the Firebirds this summer.
Complicating things for New Zealand teams, though, is that there's no guarantee English county clubs will release their players if a major association team qualifies for the Champions League.
Ross said while CD would make a concerted effort in the one-day Ford Trophy campaign in March, they would be picking a team for the next three Shield games.
"We have a bit to play for and the boys are fired up. They are hurting as they are going through tough times and it's in those tough times when they have to show character."
While critics could argue previous coach Alan Hunt had won silverware in two seasons, it appears CD are happy with replacement Malan in his maiden Stag season.
"The results are not there but Heinrich's work has been excellent," Ross said.
Despite selection flaws, the expectation is South African Malan will be more prudent in his overall approach next summer.
Defending champions Volts are the top qualifiers after yesterday's washout.
Ther Knights could have claimed the lofty perch at a windy Hagley Oval but, instead, they stumbled by five wickets to the Wizards, gifting the Auckland Aces a mathematical chance of making the preliminary final on Friday.
The CD Hinds women's domestic campaign is on a similar track to their men as the Michael Shrimpton-coached side lost 3-0 to the Wellington Blaze in Hastings at the weekend.
With four rounds played and one to go against the Canterbury Magicians in Palmerston North this weekend, the Hinds have won just one game - a rain-reduced one-day affair (26 overs) against the Northern Spirit in Christchurch after Christmas.
The side is predominantly young after White Ferns batsmen Sara McGlashan and wicketkeeper Rachel Priest crossed the floor to Auckland Hearts and the Blaze, respectively.
McGlashan, who was dropped from the New Zealand equation for the Windies tour last October, smashed a record 131no off 63 balls against ND in a T20 match on Friday at Seddon Park.
