Reviewers Conflict of interest: failing manuscript to possibly keep dominance
The vast majority of scientists are ethical people. To claim that every single one in that group is unethical to the point that they gratuitously reject other people's papers does not comport with my view on my fellow scientists. 

My approach to getting papers rejected is to make an honest assessment of why the paper was criticized, and then to set out to write better papers. Statistically, journals reject about 2/3 of all papers, so having a world view of "My paper was just not well enough written" is at least not incompatible with empirical evidence, and I find that a far easier perspective on life than to have to assume that all of my colleagues are unethical people.

All of this isn't to say that it never happens that someone behaves unethically -- it almost certainly does -- but that the assumption that everyone does is probably wrong and, moreover, that it's not productive to think that way because there is nothing you could do about your fate if that were so. A growth mindset in which you take setbacks as an opportunity to learn and do better -- regardless of the reasons for the setback -- is, in the long run, a more productive approach.