Mr Jennings, who left the broadcaster in February, said the departure of Mr Weldon - announced today - will stem the flow of people who have gone from the company since his arrival in August 2014.
Those people included news anchor Hilary Barry, who resignation last Thursday was linked by a close associate - in an interview with the New Zealand Herald - to the number of people she had seen leave under Mr Weldon's management.
Mr Jennings said the company had always operated as a unit and Mr Weldon's approach was more individualistic.
"People in that company actually love that company. The issue for Mark is that he wasn't really a cultural fit. He, for his own reasons, wanted to develop a culture that he believed in but it ran very contrary to the culture that existed there - and it was always going to end up in a tough situation."
Mr Jennings said the cultural disconnect existed across the business from television into its digital and radio units. He said the Mediaworks business was often described as a "family" - a term he didn't personally like - but it was "a highly supportive culture and it's based on team work not individualism".
"People work very much for each other. That seemed to be very different to the way Mark saw things."
Mr Jennings said it had been difficult to be at the company during its transition - he oversaw many of the changes in news and current affairs.
The impact on him was the diminishing team spirit in the company as the culture changed.
"The culture was a no blame culture. If something did go wrong we all accepted responsibility for it. It wasn't a culture to single people out.
"It meant we were close and people were always prepared to go over and above what they were paid for and what was expected of them. The hard thing for me was to see people drop off that."
He said media was a difficult industry in which to be working. Worldwide, media companies have been hit by technology changes that undermined basic business models.
"People were coming back to the company working at 100% rather than 120% and that extra 20% is what gave 3News and other parts of the company an edge, and it also gave an incredible esprit de corp."
The main focus on departures from the company had been on public faces but Mr Weldon said staff had left from right across the business. "I don't know that news was put under more pressure than other parts. There was a perception that news wasn't as supported as it had been."
However, he said the contrast had to be seen against previous chief executives who saw news as a core strength of Mediawork's offering.
"I think Mark just saw it in the same way as other parts of the company."
While Mediaworks was a private company, its role in media meant it had a responsibility to be open about its business with the public, he said.
"If you are in the news media business you are a part of the democracy of this country and people expect you to be open and play a role in New Zealand society."
