The last thing: Why do writers bring out all these points such as insulin increase or post-exercise protein synthesis rate and so on when explaining a new product?
Well first, the individual writer may be no different than many of the scientists in actually thinking that whatever parameter is being discussed does actually show being better. I very much would expect that is the case much or probably most of the time.
It is one of the ways that I am eccentric that I keep track of what actually is being measured, what is the proof that the thing being measured must actually correspond with the thing of interest, and so forth. As mentioned, it is completely typical for, for example, a doctor who ordered an HIV test back in the day when the test did not directly measure HIV but rather antibodies to HIV, to tell a patient that they tested positive and "have HIV."
(I personally know a case where a woman was told this, who did not have HIV but only antibodies to the antigen used in the test, which can be acquired by exposure to other things. These days the test is for HIV DNA so it is fair enough to call it a test for HIV. But the old test was not, it was a test for HIV antibodies, yet doctors widely did not understand what was being tested. Just as an example of how far wrong one can go by not knowing what is being tested and what its existence actually proves or does not prove.)
Not just to the average writer but for I would say even the very, very good ones, they don't stop and worry about whether the thing measured, for example post-exercise protein synthesis rate, really proves hypertrophy will be better. It just makes sense to them and the scientists seem to think so, so it's taken as a matter of course.
Secondly, there's the problem of oversimplification caused by deciding to mention something that most probably is really important, but simply leaving it at that rather than adding caveats about how it alone is not sufficient, and it alone is only one part of what is being accomplished. For example this happened with the I, Bodybuilder video and article and some concluding from it that the big breakthrough and the way Anaconda worked was spiking insulin, that if you knew how much insulin was spiked then you knew how effective something was, etc.
If you have someone who goes on and on like me, that sort of thing will automatically be taken care of in most cases, but if you have someone writing some suitably tight prose and having only a normal degree of attention to such things rather than a really peculiar degree, it very frequently won't be.
Lastly, why bring up these mechanisms at all if we don't know for a fact that the difference achieved in some biochemical analysis must mean the method gives better practical results?
Well first, the writer may well genuinely think or expect it does, as explained above. And in many cases there is good reason to think it important. For example, there's good reason to think that insulin is important to hypertrophy.
And second, the article winds up being short and unsatisfying if it consists of one sentence: "We tried it and found it to work better in practice."
People like reasons for why it makes sense that it ought to be better, and that's entirely reaosnable. I like reasons for why something plausibly ought to be better, as well.
But unlike many, despite being a published scientist with some I think quite decent science done very rigorously, myself I don't care if there is no evidence why something works or doesn't work.
For example, one of the endurance athletes we work with had a very interesting finding, involving very high dose of a given herb, that worked very well for him -- remarkably well -- and also for at least one other (I don't recall) that he recommended it to. I was asked to find whatever evidence there might be for why it might work. And also to see if there were any known reasons why there should be concern on the dosage.
The herb is well known and there are many studies on it, though none for that application. There isn't a shred of known information about how it works that makes a lick of sense to me as to how it could help an endurance athlete's performance.
But if worked well for a broader number of endurance athletes than just the 2 or 3 that had tried it, the only reason it would matter to me in the slightest that we could find no mechanism for why, is that I'd like to learn it. But I wouldn't doubt its performance from that: only its performance in practice would have me doing that.
Or, quicker example: While I do know a mechanism that may explain why Proviron is a lousy muscle anabolic, either let's say I didn't, or grant that I do. Either way, the reason for my not recommending that people base their muscle-building cycles on it is not because of knowing a mechanism for why it might not work, but because practice shows it not to work.
Regardless that studies in rats say that it is an effective anabolic, more potent than testosterone.
I know that was very lengthy but I think there is a lot of depth and importance to your question.