Which approach is better for publishing in good journals?
The conference approach has multiple advantages. The conference establishes deadlines to force you to stop researching and advance towards a manuscript. The length requirement forces you to be very brutal about condensing the crux of your research. The creation of your presentation/poster requires this 100x more, especially given that how will agonize over how to present your work when you are standing there to be embarrassed by any weaknesses in it. The actual presentation experience produces a great deal of discussion and feedback helping you understand how other researchers see your research. And finally while at the conference you get rapidly exposed to a broad range of related research, which is of immense value to both students and researchers in the field. Note that all of these can be achieved without the work being competitively peer-reviewed. Those reviews are just a bonus (assuming you get accepted in that case). 

A drawback of starting with a conference (when your ultimate goal is a journal publication) is that the journal may not accept the results as original anymore. So your journal article would need to add a significant amount of new results and/or analysis. 

As for the desk rejections, it sounds like you may not be taking them seriously enough. Consider that, as a student, when you don't understand the value in a paper or text you read, you presume the fault is your own and re-read more carefully. An editor or reviewer doesn't. They quickly skim to decide if there is any value, often starting from the assumption that there probably is not, since they don't actually want to read it anyway. If editors think your paper does not contain results, then you are failing to make the results immediately obvious. If they think your paper does not fit the scope of their journal, then you are failing to make its value within their scope immediately obvious. And the best advice for how to accomplish these things is to read the journal you want to publish in. Read it a lot. Then you will be able to explain clearly how your manuscript fits in with those other papers they publish most often.

And personally I'm not so sure the "top" journals have better reviewers. Even if they do in your field, it appears you would have a lot to gain from any reviews you can get.