In my understanding the idea of a scientific article is to be useful[.]
That is not my understanding of a scientific article (or, more basically, of science). Science is a growing body of knowledge and understanding achieved by a characteristic method, and a scientific article adds to this knowledge and understanding. (Roughly; scientific articles can also critique or falsify...) Who said it had to be useful? It is always more useful to have scientific knowledge than not to have it, and many branches of science are easily applied, but by no means all: e.g. up until relatively recently it was believed but not observed that there were exoplanets, i.e., planets outside our own solar system. The first confirmed detection of an exoplanet was in 1992. This was surely one of the major events in the history of astronomy, but...what is it useful for? Something big a thousand years from now maybe, but nothing now.
I have read some literature in the domain of my research, and almost always my critical thinking is not satisfied with what the authors have achieved in the end of their work. Somehow the conclusions seems for me not convincing.
To be honest, I am skeptical of this. Academic fields are built by intelligent, serious, hard-working people, often over the course of several lifetimes. What counts as methodological rigor in one academic field may not in another, but that's not the same thing. If as a mid-career grad student you find that most of the papers you are reading are pointless and limited in a way that you think you see through...anything is possible, but I am going to guess that you are missing something.
Is it just an impression of a sceptic or it could be that my subfield of research has reached the point where it has closed on itself (producing papers not to investingate real problems but just to keep the field afloat alrhough it has no potential for anything innovative)?
I have not in my lifetime met a scientific (or other academic) field where the grad students can tell that nothing deep is going on. It is true that different fields at different times progress in different ways: periods of fundamental advances alternate with periods of more modest improvements and aggregation of knowledge. But they all survive.
To me it sounds like you are just not intellectually interested in your academic field (or the sub-sub-... part of it you're currently occupied). You write:
I am just starting to doubt that research itself has some special value, as it seemed to me in my idealistic view when I just started my PhD. At this point I am overwhelmed with the thought that the years that I am spending on my PhD eventually will result with a similar contribution, there will be no use or value of which. May be except to support my supervisor's career and add to the mess of the literature of my domain where I already have sunk.
In my experience, younger students tend to idealize and elevate academic research as though it were something sacred. When I was a young student of mathematics, I explained why I liked mathematics in terms of its objectivity, its timelessness, and so forth. I don't say much of that anymore -- and not really because I don't believe it: I still do. But I don't believe that it explains why I did mathematics, because the explanation is not enough. There is a lot of mathematics out there; I try to appreciate all of it, but I don't do all of it. Obviously I did not become a number theorist rather than a differential geometer because number theory is more objective or timeless -- or useful! -- than differential geometry. I became a number theorist because I like (and understand, and have a proclivity for) number theory more than differential geometry. There's an ineffability there that we may as well be honest about.
I hope you see the point of that personal digression: I suspect that you simply are not interested in your subfield of applied CS and are therefore searching for more sweeping intellectual explanations of that. But you don't need to -- if you don't like it, you don't like it, and that has to be respected, in particular by you. No, you should not continue in a field just to bolster your supervisor's research career. So it's probably time for a change: whether a small change or a big change I leave up to you, but an intellectual defense of the value of Academic Field X is almost certainly not the answer.