Last month the Herald reported Petrie and Dallow were having to reapply for the same role as sole newsreader.
While it's unclear whether TVNZ bosses have spoken with Dallow, Ralston questions whether Covid-19 was a valid reason for the move or whether it was time to simply give the time slot a refresh.
"I think so.
"They'll save a couple of hundred thousand I'm sure, saying goodbye to Wendy by the sounds of it, but are they that hard up?
"I can understand because of the financial pressures and they could save a reasonably sized chunk of money by returning to one presenter ... my guess is, I can't see it as a cost-saving measure, particularly."
Changing the presenter line-up for the 6pm news was a "brave act", Ralston said, but it depended on who they put in the role.
"It depends who they put back in there. Is it Simon? I notice in Simon's absence they've been using Jack Tame, they've been using John Campbell and Melissa [Stokes] as well. They will be watching the ratings."
Ratings were no longer refreshed by the hour or quarter, rather by the minute, giving bosses an unabashed look at their viewer's movements.
"You can actually see, when a story comes on or a presenter comes on, do the ratings increase or do they decrease and they will be toying with that to see what effect the presenters have had.
"It is a fairly momentous change, you've had 14 years of the same thing and viewing is a habit but it's also what you become used to."
The 6pm news hour used to be biggest breadwinner for the station, he said.
"Obviously times have changed, television advertising has drifted away a lot, but it would still be, I would think, the biggest single earner for TVNZ."
It could also be that TVNZ was brimming with confidence and wasn't bothered about what Newshub was doing and its current dual presenter role.
"I don't know, maybe they perceive that TV3 news is not a real threat to them at the moment. I haven't seen the ratings for years but I presume TV1's must be pretty bloody solid."
If it did revert to a single presenter there were still two others - sports and weather presenter - in the mix which didn't make it an "unsupportable burden".
"You do at least have three people through the hour and it's not an unsupportable burden but I do think that Simon and Wendy were a pretty good act for 14 years.
"It's a brave act to suddenly change the way the news looks, simply because you can shake people loose ... to mess around with it too much would make me nervous if I was doing it."
Asked whether TVNZ could have been grooming Q + A presenter Jack Tame for the role the past few years, Ralston said "oh yeah and justifiably so, too".
However, he wouldn't be pressed on whether a man or a woman would be the network's preferred option.
"It's always a problem that. What gender would have the most appeal, it's tough to tell."
