"You can't buy the experience of Ben Stokes, Jos Buttler, Jonny Bairstow, Moeen Ali -- those kind of players make a big difference," Cook added.
While injuries to key players such as pacer Jofra Archer and all-rounder Ben Stokes have not helped, the problems for England compounded due to the breaks being given to the likes of Jos Buttler, Jonny Bairstow, Chris Woakes, Moeen Ali and Mark Wood.
"The decisions don't seem like they've been made correctly," said England's all-time leading Test run-scorer, Cook, who had retired in 2018.
"I've been on the other side, where you're trying to make decisions for the right reasons, but you get judged on your results by it, don't you?
"It was going so well, winning Test series at home, then Sri Lanka away and 1-0 up against India. Then you rest and rotate players, and ever since that moment on it's been chasing their tail a little bit."
Stokes, who had broken his finger during the IPL, has recently returned to action with a stint for Durham and Cook said it will provide a much needed balance to the side ahead of the India series.
"It will be a better side with the players coming back against India," said Cook, who has scored 12,472 runs in 161 Tests.
"They'll clearly be better balanced which, I think, is a massive issue for them and forced some strange selections against New Zealand, like no spinner on a dry wicket."
Cook, who led England in 59 Tests before handing the reins to Root in 2016, said fortunately he "never had to captain during a pandemic"
"...I didn't even know what a pandemic was when I was captain -- but you've got a Test captain who hasn't been able to play his best side."
England will take on India in a Test series at home next and Cook warned against any drastic changes to the top order comprising Dom Sibley, Zak Crawley, Ollie Pope and Dan Lawrence.