The line is drawn by the community themselves. They decide what the rules for the category are.

This is how all speedrunning communities work. They make rules for each category. Mods aren’t the only thing that can skip large chunks of a game. Major glitches are as well. Many, many speedrun categories prohibit major glitches that skip large sections of the game.

As @chonglibloodsport@lemmy.world says, the community draws the line, and that's the point of having a variety of categories. Plus, Speedrunning is not a hard-and-fast ruleset... only if you want to participate in the community leaderboards do you actually need to abide by the "rules," otherwise speedrunning is whatever you want it to be. If you want to sit there and mash through the cutscenes each time, go ahead and you've just made your own category and can set the world record in it. ;)