I am absolutely certain that media has a powerful influence on the way people think and that much of it is based on the beliefs, politics and agendas of their owners.
The media influencing people is a different point and I agree with you. Of course if you loved (eg) Prince Harry or Meghan and then you read a lot of negative press, it is perfectly possible your view would change due to media influence.
That's not what we were discussing though. We were discussing whether in principle what goes into a newspaper is editor/media driven agenda or not.
In other words, does (to take an example) negative press about Meghan or Prince Harry arise because "the media" (or a particular paper or editor or group of journalists) sit down and decide 'we hate Harry' or 'we aren't liking Meghan this week' lets write lots of negative things'.
Or does it arise because a lot of the readership have negative views and don't want to read wall-to-wall paeans and applause about them - that this would be a turn off to the readership so the criticisms reflect general public thinking of the readership.
I am saying that a lot of people believe (not talking about Harry particularly here but more widely) that newspapers operate in the former way and this is an urban myth. The reality is that mostly (I accept there are some exceptions as I have said) news agendas for particular papers (as they appear) arise because it is driven by what they think their readers already think or want to hear.
and that much of it is based on the beliefs, politics and agendas of their owners.
Again a different point. It is broadly true that someone right wing is unlikely to own a left wing newspaper. I also agree that an editor will typically want to avoid antagonising or upsetting their ultimate boss/owner. But these are more broad brush than actual day-to-day agenda setting issues.
Besides, most newspapers are corporations who have duties to their share holders and generally operate at arms length from the editor.
This is because freedom of expression is regarded as an important part of the business.
More practically, post- Leveson (because of the potential for criminal charges) owners are generally advised to have a completely hands-off approach to editorship. To be fair I think this was mostly done anyway. If there is a risk that criminal activity was endemic in a paper you owned and you are seen to be interferring in the paper content, then you are at risk.