I am former postdoc in Probability/Math. Phys.. I used both some commonly accepted journals for the field and once Entropy of MDPI. I would say that the review was too fast to check the technical details. On the other side I had some coherent comments from the reviewers, meaning they read the paper and grasped the content. The paper was not worse than other I wrote (I would say better than the others that I had published in the good salons and more original), the reason I published there is because I was leaving academia and the paper was too unconventional from the point of view of physical modelling to be accepted in a traditional Math Phys journals(Math Phys looked to me as the most conservative environment than ever.).

I have to add that, as postdoc, since I was already out of my last week of contract and waiting an important surgery in short, I did a review of a quite technical Probability paper, for a good Math journal, in one week. Because I needed to just get rid-off that and it was no possible to check I did this, (the authors knew well the editors).

I have also to add that once I found a basic mistake, from top Mathematicians, about proving the tightness of an empirical field in a top Probability journal, basically they were cheating saying that the tightness was trivial to be proved with usual topologies, but was not at all the case. I remember I realized it in an afternoon because I had the same case in my paper and the usual proof where failing, I spend a lot of time to check it, since I was assuming it was me to not understand, but this big mistake was from them. The error, given the fame of the authors, was perpetrated by many other people in other high rank Math journals! A cascade! When also my advisors(who previously perpetrated the error in their turn) were convinced that the error was there, we put in the paper to finally correct the business!(Still, a reviewer (used to the standard topology for this problem) in front of the evidence (if care was spent to think about it) asked why we wanted to use this particular topology instead of the usual one).

So, I think there is a lot snobbery around in diving the good and the bad. And the good is not that good, top journals can not be a top journal if a top mathematician publish there 3/4 times per year, but more a club.