You can semi-reliably cheese a lot of rooms if you can hit the shotgun grenade with the red railgun. Granted, that’s also really goddamn hard and you can get fucked really badly by the room geometry.
Hence, my point. It's all too damn much, and it's all a level of ever-increasing complexity (due to the nature of newer shit being added on top of shit that was already working just fine before) that doesn't even need to be that way to stay fun and enjoyable.
Cheese should be more along the lines of "easier than you thought, might require a little practice to get right" rather than "here's your full room nuke that you need a certain degree of speed, precision, and SEVERAL inputs all at once to accommodate, and it may not even work in most cases because the conditions aren't often right for it".
Ultrakill is functionally the equivalent of say... "In order to maximize damage on the Cyberdemon, do circular zigzag strafing in a very specific pattern, making sure you hotkey swap to the SSG for close range shots, quickly pepper with a hotswap to Chaingun while you're zigzagging away, quickly fire off a rocket or two once you're at max distance, then keep maintaining this pattern all while making sure you're not close enough to get hit by your splash damage or eat a Cyberdemon rocket. The Cyberdemon will die in no time. Also this won't work in most situations depending on the room layout or what other enemies are surrounding you."
Proper cheese, at least IMO, would be more along the lines of "Get up in the Cyberdemon's face and fire off a BFG, and stay in the Cyberdemon's face as best as you can so that all the tracers hit the Cyberdemon. It will usually die in 1-2 shots this way." It's simple, effective, and requires less practice than what's mentioned above. It can also be very situational as well, but it DOES generally work in most situations.