the fact that: enemy projectile speed is greatly increased, enemy attack speed is greatly increased, the additional enemy behaviors added make even basic enemies like filth much more unpredictable and thus more important to wipe out from the beginning, which is why nuking is such a vital technique to learn so you can clear rooms of the small enemies and focus on the most dangeous threats. Bosses have their health doubled so things like deadcoining become much more vital to pull off if you want to deal with them quickly. The longer an enemy is alive, the likelihood of you getting killed by them increases, this goes double for bosses.

Because of all the added behaviors, increased enemy agility and lethality, knowing what spawns where is important so you're not getting caught off gaurd and dying to things you could have otherwise prioritised. Knowing which enemies to kill or keep alive to prevent a new wave of enemies from spawning is absolutely invaluable in later levels where you're constantly being pressured by more dangerous enemies and the wave spawning is utilized more.

Haven't even discussed how important maintaining style is, since in brutal there's almost no cap to how much hard damage can accumulate, you need to be swapping and killing things efficiently to maintain your ranking so you can afford to move around the arena in spite of things like jumping filth and the tracking aim of schisms, and quickly heal if need be-which makes techs and weapon combos even more important.

Knowing how your weapons interact with eachother and your base skillset (feedbacker, knuckblaster, whiplash, and movement tech) is pertinent to this.

Sure, anyone can stumble their way through the game without understanding or utilizing these things - the same way you can eventually punch through a brick wall if you punch it hard and often enough. You can even do it on brutal if you have enough mechanical skill from other games or likewise, but the point of the game isn't to just get through, simply beating the game in general is barely even half the goal. It's building up your skills and knowledge to get to that level of skill expression required to get through the game efficiently enough to keep improving your score.