There is certainly an element of luck involved, but it is much, much better than it used to be. When I came through at level 4 the marks ranged from 50 to 95. I had one game where I didn't think I'd done much, no KMD's, only a couple of cautions, and I got 84. The following game I had several KMDs, got them all right, got nothing wrong, and got 72. Marks that far apart made a huge difference, you could change 3 bands just on the basis of one performance. I didn't go up one season with an average of over 79, the following season I finished top with an average of over 80, but I am the first to admit I got lucky as if I'd had just one low marker, like the one that gave me 72 in an earlier season, I'd have missed out. I suspect the league were looking after me with the observers as they knew just how disappointed was not to go up the previous season (one game had killed me). My marks in the promotion season were 80,84,82,79,79,80, obviously there is zero chance of getting marks like that these days.
The answer, in my opinion, is to move to FIFA style marking, like they use in almost every other country. The problem with that though is an incorrect KMD is a disaster, and without video evidence it is very much the observer's opinion versus yours.