I think about this in terms of what makes the greatest difference to my shaving experience on a variable basis. For example, my pre-shave routine is very important but I have long settled on it and I do the same thing every time, washing with a glycerine or clay soap. Same with blades - I settled on a few that I like best and I just use those and never have to think about the blade.
So I would say what really makes a difference from shave to shave is (1) the razor, by far, (2) the soap - lather quality and scent, and (3) the brush. The reason I have brushes third is that I have many good brushes that feel good to me and largely similar, and I’m not normally shifting from a soft knot to a scritchy knot. I do use different fibres, different sizes, etc. but it’s not really a massive difference for my shave.
So I would say what really makes a difference from shave to shave is (1) the razor, by far, (2) the soap - lather quality and scent, and (3) the brush. The reason I have brushes third is that I have many good brushes that feel good to me and largely similar, and I’m not normally shifting from a soft knot to a scritchy knot. I do use different fibres, different sizes, etc. but it’s not really a massive difference for my shave.