You've asked a wonderful question, Che. It connects well to the themes that have been popping-up lately in my own practice.
In my experience, there are many different strategies that we develop to train our minds. This happens naturally for anyone who is practicing intelligently and paying attention. (i.e., you will creatively look for ways to make your meditation "work," even if that means doing things that a teacher had not taught you).
Like an artist who develops different techniques for holding a brush, we develop different ways to quiet the mind and direct our awareness. Personally, I have found that every time I figure out a new way that works, I cling to it, and say THIS is THE way to meditate. For example, I remember when I discovered how I could calm the mind by stilling my eyes, and cultivating a spacious visual field. Amazingly that works sometimes. (remember when you figured out the same thing? I recall you frequently posting about it!

). After I make such a "discovery," I will stick to it for awhile, and be really excited about it. And it works!
But then, inevitably, it
stops working! And then the question is, how long do you aimlessly space out because you've lost samadhi, and the usual "trick" isn't working? Maybe you get frustrated? Maybe you just drift lazily? Maybe you just wait around for the old "trick" to start working again. (but who knows how long that can take?)
Ultimately, I have come to see that this tendency to believe that there is ONE way to attain samadhi is based on a delusion of permanence. It is from ignorance that we think one way will
always work. It is from ignorance that we believe that the mind is a fixed static thing that can be trained with one approach.
The reality for myself is that different approaches work at different times, some more than others, but they are all good. Sometimes I may focus on watching my awareness, anticipating the arising of thoughts (perhaps this is what you call the gatekeeper?).
Or I may focus on my intentions. I find that reflecting on my practice and what
really matters can make most thoughts seem petty and unimportant so they naturally lose their attraction.
Sometimes, I bring my awareness fluidly throughout the body, finding that this concentrates me when the breath does not.
Other times, I find that really watching the breath is the best way to concentrate. Sometimes, I find it really helpful to focus on the gap between the in-breath and out-breath (as this is where the mind typically wanders).
Or I find that I benefit by focusing on the breath in different places. (the abdomen, the chest, or the entire body brings me a
spacious awareness. A small point below my nostrils brings a
sharp awareness)
Sometimes, I find
remembering a previous experience of samadhi will help trigger that state. In fact, I think that for many of us, we just need to enter this state enough times, and then eventually, we enter it with greater ease, and without much need for tricks.
I could go on, but I obviously subscribe to the "free-style" approach.

But each one of us has to figure out the methods that work for us, and actually use them, and re-use them, and let them go, and then return to them.
With metta,
KN