To set some context, I can’t see the photo you’re asking about. The linked question links to a site that I cannot access due to firewall restrictions. I’ve assumed that you’re the photographer.
What can be identified as a subject in a landscape photograph comprising of things which are
The photographer determines the subject of the photograph. If all things are equally important, to the photographer, then there is nothing wrong with them being the subject of the photograph. The question seems very similar to asking how to identify the subject of a family portrait. Is it the dad, the mom, the baby? If they’re all equally important, then the subject is the family. However, an individual within the scene could be more important to the photographer and could be emphasised as the subject by changing the composition (framing, lighting, DoF...).
How do you decide the subject when you have to photograph a scene containing a house, tree, row
of trees, sky - all together. All of these form the scene all together IMO.
Is these kind of cases, it is still necessary to segregate a particular item rather then make appear
everything equally important?
No, if you as the photographer like the scene as is, you don’t have to decide to emphasise a particular object. If the collection is the subject and it works for you, that is what is important.
Can composition be improved somehow
Most photographers are going to have a different view on what makes great composition, each individuals perspective will suggest some change to a photograph that might have made it sit better for them. That doesn’t mean the photograph is wrong, or that they’re right. It just means that people like different things.
here so that one doesn't feel like asking what is the subject?
Almost certainly not. Somebody, somewhere, will eventually ask what’s that a photograph of, where is it, why did you take that photo. People have different tastes / likes; this is particularly true on the internet where cultural differences can have significant impact. There are few landscape pictures that are going to touch somebody that doesn’t like landscapes. Whilst it’s an admirable goal, it’s not going to be an easy one to achieve and I would suggest is likely to stem from you doing something that takes them by surprise.