It was rare for Trevor to operate outside of a structured bulletin. But, he could do if necessary. No doubt.
Going back to BBC and Clive: totally agree with everyone here. He’s been out on the road for years and that, for me, lends so much than just sitting behind a desk and reading.
As you mention, all of the above have similar experiences in their own respective fields.
ITN deliberately made a point of alternating people between presenting and reporting, to emphasise to the audience that they weren't just reading a script but had credibility and experience. Some didn't enjoy it much, though, I know Michael Nicholson said he didn't really like newsreading and was always itching to get back to reporting. But as you say, Trevor McDonald had vast experience as a reporter before he became the main anchor.
I believe when the ITN News Channel launched in 2000, many newscasters were given the option to take up a role on it. Some jumped at it, like John Suchet. But others turned it down. I can only imagine that Trevor turned it down if he was asked - I couldn't see him handling rolling news very well. It just wasn't his strength.
I remember an interview with John Suchet at the time saying he jumped at the chance to go on the ITN News Channel because he was convinced the future of news was rolling news, and had been desperate to ITN to launch a channel.