I think this is so antithetical to the game design and it sounds like you fundamentally don't understand it. The additional enemies are there so you can recharge health and armor, and the line of sight breaks are for your sake, not the enemy's.
I think you misunderstood my post. I get the rules of the game and the intent behind the fodder, but that is not what I was talking about.
Did you fight the boss? You have to lean on the Pulse rifle to melt their shields in a sustained amount of fire for a brief window or else it recharges. The two bosses also scramble around corners, hopping up platforms, etc... this breaks your line of sight as you pursue opportunity to fire. Meanwhile doing this, an army is at your back(not just the meager zombies that are clearly designed for resource gathering) but imps, shield guys, teleporting phase demons, gargoyles, etc... all the things that can melt you down fast while your focus is elsewhere.
So this led to scrambling them down to provide a reprieve to focus fire and chase my true target without off-screen fuckery. But also given the tight arena with walled zones(which -yes- do help defensively), also can be disruptive when dashing away from a flurry of fire leading to more deaths being caught on geometry than the threat of the foe itself I was facing. My point is that death often resulted from getting caught on something, or three things spawning behind me that I didn't notice. Not the true foe.
I managed through it. I played as intended and it worked out, it just felt tedious instead of exhilerating.