I think the main problem with fakeout endscreens is that to anyone who's familiar with GD they are usually not convincing due to any small imperfections or inaccuracies within the endscreen animation or UI, this issue only really being able to be neutralised through near inhuman technical skill. Obviously most people don't have that, and the fact that the last bossfight only lasts for less than 10 seconds hurts the overall level quality even more. What is inhuman, though, is the cohesion of every single part which is an insane technical feat but that unfortunately doesn't translate well into level quality as this could very well be a solo with similar effect (not including the time constraint)